Fix polymorphic element types usage; Empty `union` as opaque type

14 files changed, 228 insertions, 170 deletions

diff --git a/code/demo.odin b/code/demo.odin
index 4d87bbfec..912168306 100644
--- a/code/demo.odin
+++ b/code/demo.odin
@@ -1,6 +1,11 @@
 import "fmt.odin";
+import "strconv.odin";
+
+Opaque :: union{};
 
 main :: proc() {
-	fmt.println("Hellope!");
+	buf := make([]u8, 0, 10);
+	s := strconv.append_bool(buf, true);
+	fmt.println(s);
 }
 
diff --git a/core/_preload.odin b/core/_preload.odin
index af0a9270d..316b5b2f1 100644
--- a/core/_preload.odin
+++ b/core/_preload.odin
@@ -314,7 +314,6 @@ copy :: proc(dst, src: $T/[]$E) -> int #cc_contextless {
 }
 
 
-
 append :: proc(array: ^$T/[]$E, args: ...E) -> int #cc_contextless {
 	if array == nil do return 0;
 
@@ -356,6 +355,19 @@ append :: proc(array: ^$T/[dynamic]$E, args: ...E) -> int {
 	return len(array);
 }
 
+append :: proc(array: ^$T/[]u8, args: ...string) -> int {
+	for arg in args {
+		append(array, ...cast([]u8)arg);
+	}
+	return len(array);
+}
+append :: proc(array: ^$T/[dynamic]u8, args: ...string) -> int {
+	for arg in args {
+		append(array, ...cast([]u8)arg);
+	}
+	return len(array);
+}
+
 pop :: proc(array: ^$T/[]$E) -> E #cc_contextless {
 	if array == nil do return E{};
 	assert(len(array) > 0);
diff --git a/core/fmt.odin b/core/fmt.odin
index 0c0ecf4f4..c8723f6c4 100644
--- a/core/fmt.odin
+++ b/core/fmt.odin
@@ -186,7 +186,8 @@ write_type :: proc(buf: ^StringBuffer, ti: ^TypeInfo) {
 		case ti == type_info_of(int):  write_string(buf, "int");
 		case ti == type_info_of(uint): write_string(buf, "uint");
 		case:
-			write_string(buf, info.signed ? "i" : "u");
+			if info.signed do write_byte(buf, 'i');
+			else           do write_byte(buf, 'u');
 			write_int(buf, i64(8*ti.size), 10);
 		}
 	case Rune:
@@ -424,7 +425,9 @@ fmt_bad_verb :: proc(using fi: ^FmtInfo, verb: rune) {
 fmt_bool :: proc(using fi: ^FmtInfo, b: bool, verb: rune) {
 	match verb {
 	case 't', 'v':
-		write_string(buf, b ? "true" : "false");
+		s := "false";
+		if b do s = "true";
+		write_string(buf, s);
 	case:
 		fmt_bad_verb(fi, verb);
 	}
@@ -434,7 +437,8 @@ fmt_bool :: proc(using fi: ^FmtInfo, b: bool, verb: rune) {
 fmt_write_padding :: proc(fi: ^FmtInfo, width: int) {
 	if width <= 0 do return;
 
-	pad_byte: u8 = fi.space ? ' ' : '0';
+	pad_byte: u8 = '0';
+	if fi.space do pad_byte = ' ';
 
 	for _ in 0..width {
 		write_byte(fi.buf, pad_byte);
@@ -569,7 +573,8 @@ fmt_float :: proc(fi: ^FmtInfo, v: f64, bit_size: int, verb: rune) {
 	// case 'f', 'F', 'v':
 
 	case 'f', 'F', 'v':
-		prec: int = fi.prec_set ? fi.prec : 3;
+		prec: int = 3;
+		if fi.prec_set do prec = fi.prec;
 		buf: [386]u8;
 
 		str := strconv.append_float(buf[1..1], v, 'f', prec, bit_size);
@@ -617,7 +622,9 @@ fmt_string :: proc(fi: ^FmtInfo, s: string, verb: rune) {
 
 		for i in 0..len(s) {
 			if i > 0 && space do write_byte(fi.buf, ' ');
-			_fmt_int(fi, u128(s[i]), 16, false, 8, verb == 'x' ? __DIGITS_LOWER : __DIGITS_UPPER);
+			char_set := __DIGITS_UPPER;
+			if verb == 'x' do char_set = __DIGITS_LOWER;
+			_fmt_int(fi, u128(s[i]), 16, false, 8, char_set);
 		}
 
 	case:
diff --git a/core/math.odin b/core/math.odin
index bf85b5026..04af9593a 100644
--- a/core/math.odin
+++ b/core/math.odin
@@ -54,8 +54,8 @@ unlerp :: proc(a, b, x: f32) -> (t: f32) do return (x-a)/(b-a);
 unlerp :: proc(a, b, x: f64) -> (t: f64) do return (x-a)/(b-a);
 
 
-sign :: proc(x: f32) -> f32 do return x >= 0 ? +1 : -1;
-sign :: proc(x: f64) -> f64 do return x >= 0 ? +1 : -1;
+sign :: proc(x: f32) -> f32 { if x >= 0 do return +1; return -1; }
+sign :: proc(x: f64) -> f64 { if x >= 0 do return +1; return -1; }
 
 
 
@@ -75,14 +75,14 @@ copy_sign :: proc(x, y: f64) -> f64 {
 	return transmute(f64, ix);
 }
 
-round :: proc(x: f32) -> f32 do return x >= 0 ? floor(x + 0.5) : ceil(x - 0.5);
-round :: proc(x: f64) -> f64 do return x >= 0 ? floor(x + 0.5) : ceil(x - 0.5);
+round :: proc(x: f32) -> f32 { if x >= 0 do return floor(x + 0.5); return ceil(x - 0.5); }
+round :: proc(x: f64) -> f64 { if x >= 0 do return floor(x + 0.5); return ceil(x - 0.5); }
 
-floor :: proc(x: f32) -> f32 do return x >= 0 ? f32(i64(x)) : f32(i64(x-0.5)); // TODO: Get accurate versions
-floor :: proc(x: f64) -> f64 do return x >= 0 ? f64(i64(x)) : f64(i64(x-0.5)); // TODO: Get accurate versions
+floor :: proc(x: f32) -> f32 { if x >= 0 do f32(i64(x)) return f32(i64(x-0.5)); } // TODO: Get accurate versions
+floor :: proc(x: f64) -> f64 { if x >= 0 do f64(i64(x)) return f64(i64(x-0.5)); } // TODO: Get accurate versions
 
-ceil :: proc(x: f32) -> f32 do return x <  0 ? f32(i64(x)) : f32(i64(x+1)); // TODO: Get accurate versions
-ceil :: proc(x: f64) -> f64 do return x <  0 ? f64(i64(x)) : f64(i64(x+1)); // TODO: Get accurate versions
+ceil :: proc(x: f32) -> f32 { if x <  0 do f32(i64(x)) return f32(i64(x+1));  }// TODO: Get accurate versions
+ceil :: proc(x: f64) -> f64 { if x <  0 do f64(i64(x)) return f64(i64(x+1));  }// TODO: Get accurate versions
 
 remainder :: proc(x, y: f32) -> f32 do return x - round(x/y) * y;
 remainder :: proc(x, y: f64) -> f64 do return x - round(x/y) * y;
@@ -133,17 +133,20 @@ norm :: proc(v: $T/[vector 4]$E) -> T do return v / mag(v);
 
 norm0 :: proc(v: $T/[vector 2]$E) -> T {
 	m := mag(v);
-	return m == 0 ? 0 : v/m;
+	if m == 0 do return 0;
+	return v/m;
 }
 
 norm0 :: proc(v: $T/[vector 3]$E) -> T {
 	m := mag(v);
-	return m == 0 ? 0 : v/m;
+	if m == 0 do return 0;
+	return v/m;
 }
 
 norm0 :: proc(v: $T/[vector 4]$E) -> T {
 	m := mag(v);
-	return m == 0 ? 0 : v/m;
+	if m == 0 do return 0;
+	return v/m;
 }
 
 
diff --git a/core/strconv.odin b/core/strconv.odin
index dbe7c20fb..a4a7a43f1 100644
--- a/core/strconv.odin
+++ b/core/strconv.odin
@@ -67,7 +67,8 @@ parse_i128 :: proc(s: string) -> i128 {
 		value += v;
 	}
 
-	return neg ? -value : value;
+	if neg do return -value;
+	return value;
 }
 
 parse_u128 :: proc(s: string) -> u128 {
@@ -91,19 +92,15 @@ parse_u128 :: proc(s: string) -> u128 {
 
 	value: u128;
 	for r in s {
-		if r == '_' {
-			continue;
-		}
-
+		if r == '_' do continue;
 		v := u128(_digit_value(r));
-		if v >= base {
-			break;
-		}
+		if v >= base do break;
 		value *= base;
 		value += u128(v);
 	}
 
-	return neg ? -value : value;
+	if neg do return -value;
+	return value;
 }
 
 
@@ -127,6 +124,7 @@ parse_f64 :: proc(s: string) -> f64 {
 	for ; i < len(s); i += 1 {
 		r := rune(s[i]);
 		if r == '_' do continue;
+
 		v := _digit_value(r);
 		if v >= 10 do break;
 		value *= 10;
@@ -139,13 +137,10 @@ parse_f64 :: proc(s: string) -> f64 {
 
 		for ; i < len(s); i += 1 {
 			r := rune(s[i]);
-			if r == '_' {
-				continue;
-			}
+			if r == '_' do continue;
+
 			v := _digit_value(r);
-			if v >= 10 {
-				break;
-			}
+			if v >= 10 do break;
 			value += f64(v)/pow10;
 			pow10 *= 10;
 		}
@@ -165,13 +160,10 @@ parse_f64 :: proc(s: string) -> f64 {
 		exp: u32 = 0;
 		for ; i < len(s); i += 1 {
 			r := rune(s[i]);
-			if r == '_' {
-				continue;
-			}
+			if r == '_' do continue;
+
 			d := u32(_digit_value(r));
-			if d >= 10 {
-				break;
-			}
+			if d >= 10 do break;
 			exp = exp * 10 + d;
 		}
 		if exp > 308 { exp = 308; }
@@ -181,13 +173,17 @@ parse_f64 :: proc(s: string) -> f64 {
 		for exp >   0 { scale *=   10; exp -=  1; }
 	}
 
-	return sign * (frac ? (value/scale) : (value*scale));
+	if frac do return sign * (value/scale);
+	return sign * (value*scale);
 }
 
 
 append_bool :: proc(buf: []u8, b: bool) -> string {
-	s := b ? "true" : "false";
-	append(&buf, ...cast([]u8)s);
+	if b {
+		append(&buf, "true");
+	} else {
+		append(&buf, "false");
+	}
 	return string(buf);
 }
 
diff --git a/src/array.cpp b/src/array.cpp
index b382d3262..c1e47342c 100644
--- a/src/array.cpp
+++ b/src/array.cpp
@@ -10,12 +10,16 @@ struct Array {
 	isize       capacity;
 
 	T &operator[](isize index) {
-		GB_ASSERT_MSG(0 <= index && index < count, "Index %td is out of bounds ranges 0..<%td", index, count);
+		#if !defined(NO_ARRAY_BOUNDS_CHECK)
+			GB_ASSERT_MSG(0 <= index && index < count, "Index %td is out of bounds ranges 0..<%td", index, count);
+		#endif
 		return data[index];
 	}
 
 	T const &operator[](isize index) const {
-		GB_ASSERT_MSG(0 <= index && index < count, "Index %td is out of bounds ranges 0..<%td", index, count);
+		#if !defined(NO_ARRAY_BOUNDS_CHECK)
+			GB_ASSERT_MSG(0 <= index && index < count, "Index %td is out of bounds ranges 0..<%td", index, count);
+		#endif
 		return data[index];
 	}
 };
diff --git a/src/check_decl.cpp b/src/check_decl.cpp
index dbe8aac61..6c550809c 100644
--- a/src/check_decl.cpp
+++ b/src/check_decl.cpp
@@ -65,6 +65,12 @@ Type *check_init_variable(Checker *c, Entity *e, Operand *operand, String contex
 			error(e->token, "Invalid use of a polymorphic type `%s` in %.*s", str, LIT(context_name));
 			e->type = t_invalid;
 			return nullptr;
+		} else if (is_type_empty_union(t)) {
+			gbString str = type_to_string(t);
+			defer (gb_string_free(str));
+			error(e->token, "An empty union `%s` cannot be instantiated in %.*s", str, LIT(context_name));
+			e->type = t_invalid;
+			return nullptr;
 		}
 		if (is_type_bit_field_value(t)) {
 			t = default_bit_field_value_type(t);
@@ -558,11 +564,18 @@ void check_var_decl(Checker *c, Entity *e, Entity **entities, isize entity_count
 	if (type_expr != nullptr) {
 		e->type = check_type(c, type_expr);
 	}
-	if (e->type != nullptr && is_type_polymorphic(base_type(e->type))) {
-		gbString str = type_to_string(e->type);
-		defer (gb_string_free(str));
-		error(e->token, "Invalid use of a polymorphic type `%s` in %.*s", str, LIT(context_name));
-		e->type = t_invalid;
+	if (e->type != nullptr) {
+		if (is_type_polymorphic(base_type(e->type))) {
+			gbString str = type_to_string(e->type);
+			defer (gb_string_free(str));
+			error(e->token, "Invalid use of a polymorphic type `%s` in %.*s", str, LIT(context_name));
+			e->type = t_invalid;
+		} else if (is_type_empty_union(e->type)) {
+			gbString str = type_to_string(e->type);
+			defer (gb_string_free(str));
+			error(e->token, "An empty union `%s` cannot be instantiated in %.*s", str, LIT(context_name));
+			e->type = t_invalid;
+		}
 	}
 
 
diff --git a/src/check_expr.cpp b/src/check_expr.cpp
index 23c823186..cd467cce1 100644
--- a/src/check_expr.cpp
+++ b/src/check_expr.cpp
@@ -149,8 +149,7 @@ bool check_is_assignable_to_using_subtype(Type *src, Type *dst) {
 }
 
 bool find_or_generate_polymorphic_procedure(Checker *c, Entity *base_entity, Type *type,
-                                            Array<Operand> *param_operands, PolyProcData *poly_proc_data,
-                                            bool check_later) {
+                                            Array<Operand> *param_operands, PolyProcData *poly_proc_data) {
 	///////////////////////////////////////////////////////////////////////////////
 	//                                                                           //
 	// TODO CLEANUP(bill): This procedure is very messy and hacky. Clean this!!! //
@@ -223,7 +222,6 @@ bool find_or_generate_polymorphic_procedure(Checker *c, Entity *base_entity, Typ
 
 
 
-
 	CheckerContext prev_context = c->context;
 	defer (c->context = prev_context);
 
@@ -238,6 +236,7 @@ bool find_or_generate_polymorphic_procedure(Checker *c, Entity *base_entity, Typ
 		// c->context.no_polymorphic_errors = false;
 	}
 
+
 	bool generate_type_again = c->context.no_polymorphic_errors;
 
 	auto *pt = &src->Proc;
@@ -251,6 +250,8 @@ bool find_or_generate_polymorphic_procedure(Checker *c, Entity *base_entity, Typ
 		return false;
 	}
 
+
+
 	auto *found_gen_procs = map_get(&c->info.gen_procs, hash_pointer(base_entity->identifier));
 	if (found_gen_procs) {
 		auto procs = *found_gen_procs;
@@ -269,7 +270,6 @@ bool find_or_generate_polymorphic_procedure(Checker *c, Entity *base_entity, Typ
 
 	if (generate_type_again) {
 		// LEAK TODO(bill): This is technically a memory leak as it has to generate the type twice
-
 		bool prev_no_polymorphic_errors = c->context.no_polymorphic_errors;
 		defer (c->context.no_polymorphic_errors = prev_no_polymorphic_errors);
 		c->context.no_polymorphic_errors = false;
@@ -283,6 +283,7 @@ bool find_or_generate_polymorphic_procedure(Checker *c, Entity *base_entity, Typ
 			return false;
 		}
 
+
 		if (found_gen_procs) {
 			auto procs = *found_gen_procs;
 			for_array(i, procs) {
@@ -298,9 +299,10 @@ bool find_or_generate_polymorphic_procedure(Checker *c, Entity *base_entity, Typ
 		}
 	}
 
+
 	AstNode *proc_lit = clone_ast_node(a, old_decl->proc_lit);
 	ast_node(pl, ProcLit, proc_lit);
-	// NOTE(bill): Associate the scope declared above with this procedure declaration's type
+	// NOTE(bill): Associate the scope declared above withinth this procedure declaration's type
 	add_scope(c, pl->type, final_proc_type->Proc.scope);
 	final_proc_type->Proc.is_poly_specialized = true;
 	final_proc_type->Proc.is_polymorphic = true;
@@ -350,16 +352,13 @@ bool find_or_generate_polymorphic_procedure(Checker *c, Entity *base_entity, Typ
 
 	GB_ASSERT(entity != nullptr);
 
-
 	if (poly_proc_data) {
 		poly_proc_data->gen_entity = entity;
 		poly_proc_data->proc_info  = proc_info;
 	}
 
-	if (check_later) {
-		// NOTE(bill): Check the newly generated procedure body
-		check_procedure_later(c, proc_info);
-	}
+	// NOTE(bill): Check the newly generated procedure body
+	check_procedure_later(c, proc_info);
 
 	return true;
 }
@@ -368,11 +367,11 @@ bool check_polymorphic_procedure_assignment(Checker *c, Operand *operand, Type *
 	if (operand->expr == NULL) return false;
 	Entity *base_entity = entity_of_ident(&c->info, operand->expr);
 	if (base_entity == nullptr) return false;
-	return find_or_generate_polymorphic_procedure(c, base_entity, type, nullptr, poly_proc_data, true);
+	return find_or_generate_polymorphic_procedure(c, base_entity, type, nullptr, poly_proc_data);
 }
 
 bool find_or_generate_polymorphic_procedure_from_parameters(Checker *c, Entity *base_entity, Array<Operand> *operands, PolyProcData *poly_proc_data) {
-	return find_or_generate_polymorphic_procedure(c, base_entity, nullptr, operands, poly_proc_data, false);
+	return find_or_generate_polymorphic_procedure(c, base_entity, nullptr, operands, poly_proc_data);
 }
 
 bool check_type_specialization_to(Checker *c, Type *specialization, Type *type, bool compound, bool modify_type);
@@ -829,6 +828,16 @@ void check_struct_field_decl(Checker *c, AstNode *decl, Array<Entity *> *fields,
 		type = t_invalid;
 	}
 
+	if (is_type_empty_union(type)) {
+		error(vd->names[0], "An empty union cannot be used as a field type in %.*s", LIT(context));
+		type = t_invalid;
+	}
+	if (!c->context.allow_polymorphic_types && is_type_polymorphic(base_type(type))) {
+		error(vd->names[0], "Invalid use of a polymorphic type in %.*s", LIT(context));
+		type = t_invalid;
+	}
+
+
 	Array<Operand> default_values = {};
 	defer (array_free(&default_values));
 	if (vd->values.count > 0 && allow_default_values) {
@@ -1836,7 +1845,7 @@ Type *determine_type_from_polymorphic(Checker *c, Type *poly_type, Operand opera
 }
 
 
-Type *check_get_params(Checker *c, Scope *scope, AstNode *_params, bool *is_variadic_, bool *success_, Array<Operand> *operands) {
+Type *check_get_params(Checker *c, Scope *scope, AstNode *_params, bool *is_variadic_, bool *success_, isize *specialization_count_, Array<Operand> *operands) {
 	if (_params == nullptr) {
 		return nullptr;
 	}
@@ -2006,6 +2015,12 @@ Type *check_get_params(Checker *c, Scope *scope, AstNode *_params, bool *is_vari
 			}
 			type = t_invalid;
 		}
+		if (is_type_empty_union(type)) {
+			gbString str = type_to_string(type);
+			error(params[i], "Invalid use of an empty union `%s`", str);
+			gb_string_free(str);
+			type = t_invalid;
+		}
 
 
 		if (p->flags&FieldFlag_c_vararg) {
@@ -2046,6 +2061,7 @@ Type *check_get_params(Checker *c, Scope *scope, AstNode *_params, bool *is_vari
 						type = t_invalid;
 					}
 					bool modify_type = !c->context.no_polymorphic_errors;
+
 					if (specialization != nullptr && !check_type_specialization_to(c, specialization, type, false, modify_type)) {
 						if (!c->context.no_polymorphic_errors) {
 							gbString t = type_to_string(type);
@@ -2105,10 +2121,25 @@ Type *check_get_params(Checker *c, Scope *scope, AstNode *_params, bool *is_vari
 		}
 	}
 
+	isize specialization_count = 0;
+	if (scope != nullptr) {
+		for_array(i, scope->elements.entries) {
+			Entity *e = scope->elements.entries[i].value;
+			if (e->kind == Type_Named) {
+				Type *t = e->type;
+				if (t->kind == Type_Generic &&
+				    t->Generic.specialized != nullptr) {
+					specialization_count += 1;
+				}
+			}
+		}
+	}
+
 	Type *tuple = make_type_tuple(c->allocator);
 	tuple->Tuple.variables = variables;
 
 	if (success_) *success_ = success;
+	if (specialization_count_) *specialization_count_ = specialization_count;
 	if (is_variadic_) *is_variadic_ = is_variadic;
 
 	return tuple;
@@ -2425,7 +2456,8 @@ bool check_procedure_type(Checker *c, Type *type, AstNode *proc_type_node, Array
 
 	bool variadic = false;
 	bool success = true;
-	Type *params  = check_get_params(c, c->context.scope, pt->params, &variadic, &success, operands);
+	isize specialization_count = 0;
+	Type *params  = check_get_params(c, c->context.scope, pt->params, &variadic, &success, &specialization_count, operands);
 	Type *results = check_get_results(c, c->context.scope, pt->results);
 
 	isize param_count = 0;
@@ -2433,15 +2465,16 @@ bool check_procedure_type(Checker *c, Type *type, AstNode *proc_type_node, Array
 	if (params)  param_count  = params ->Tuple.variables.count;
 	if (results) result_count = results->Tuple.variables.count;
 
-	type->Proc.node               = proc_type_node;
-	type->Proc.scope              = c->context.scope;
-	type->Proc.params             = params;
-	type->Proc.param_count        = param_count;
-	type->Proc.results            = results;
-	type->Proc.result_count       = result_count;
-	type->Proc.variadic           = variadic;
-	type->Proc.calling_convention = pt->calling_convention;
-	type->Proc.is_polymorphic     = pt->generic;
+	type->Proc.node                 = proc_type_node;
+	type->Proc.scope                = c->context.scope;
+	type->Proc.params               = params;
+	type->Proc.param_count          = param_count;
+	type->Proc.results              = results;
+	type->Proc.result_count         = result_count;
+	type->Proc.variadic             = variadic;
+	type->Proc.calling_convention   = pt->calling_convention;
+	type->Proc.is_polymorphic       = pt->generic;
+	type->Proc.specialization_count = specialization_count;
 
 	if (param_count > 0) {
 		Entity *end = params->Tuple.variables[param_count-1];
@@ -2886,6 +2919,10 @@ bool check_type_internal(Checker *c, AstNode *e, Type **type, Type *named_type)
 			e->TypeName.is_type_alias = true;
 			add_entity(c, ps, ident, e);
 			add_entity(c, s, ident, e);
+		} else {
+			error(ident, "Invalid use of a polymorphic type `$%.*s`", LIT(token.string));
+			*type = t_invalid;
+			return false;
 		}
 		*type = t;
 		return true;
@@ -2945,25 +2982,19 @@ bool check_type_internal(Checker *c, AstNode *e, Type **type, Type *named_type)
 				error(at->count, "... can only be used in conjuction with compound literals");
 				count = 0;
 			}
-#if 0
-			i64 esz = type_size_of(c->allocator, elem);
-			if (esz == 0) {
+			if (is_type_empty_union(elem)) {
 				gbString str = type_to_string(elem);
-				error(at->elem, "Zero sized element type `%s` is not allowed", str);
+				error(at->elem, "An empty union `%s` is not allowed as an array element type", str);
 				gb_string_free(str);
 			}
-#endif
 			*type = make_type_array(c->allocator, elem, count);
 		} else {
 			Type *elem = check_type(c, at->elem);
-#if 0
-			i64 esz = type_size_of(c->allocator, elem);
-			if (esz == 0) {
+			if (is_type_empty_union(elem)) {
 				gbString str = type_to_string(elem);
-				error(at->elem, "Zero sized element type `%s` is not allowed", str);
+				error(at->elem, "An empty union `%s` is not allowed as an slice element type", str);
 				gb_string_free(str);
 			}
-#endif
 			*type = make_type_slice(c->allocator, elem);
 		}
 		return true;
@@ -2971,14 +3002,11 @@ bool check_type_internal(Checker *c, AstNode *e, Type **type, Type *named_type)
 
 	case_ast_node(dat, DynamicArrayType, e);
 		Type *elem = check_type(c, dat->elem);
-		i64 esz = type_size_of(c->allocator, elem);
-#if 0
-		if (esz == 0) {
+		if (is_type_empty_union(elem)) {
 			gbString str = type_to_string(elem);
-			error(dat->elem, "Zero sized element type `%s` is not allowed", str);
+			error(dat->elem, "An empty union `%s` is not allowed as an dynamic array element type", str);
 			gb_string_free(str);
 		}
-#endif
 		*type = make_type_dynamic_array(c->allocator, elem);
 		return true;
 	case_end;
@@ -2989,7 +3017,11 @@ bool check_type_internal(Checker *c, AstNode *e, Type **type, Type *named_type)
 		Type *elem = check_type(c, vt->elem);
 		Type *be = base_type(elem);
 		i64 count = check_array_or_map_count(c, vt->count, false);
-		if (is_type_vector(be) || (!is_type_boolean(be) && !is_type_numeric(be) && be->kind != Type_Generic)) {
+		if (!c->context.allow_polymorphic_types && is_type_polymorphic(base_type(elem))) {
+			gbString str = type_to_string(elem);
+			error(vt->elem, "Invalid use of a polymorphic type `%s` as an dynamic array element type", str);
+			gb_string_free(str);
+		} else if (is_type_vector(be) || (!is_type_boolean(be) && !is_type_numeric(be) && !is_type_polymorphic(base_type(elem)))) {
 			gbString err_str = type_to_string(elem);
 			error(vt->elem, "Vector element type must be numerical or a boolean, got `%s`", err_str);
 			gb_string_free(err_str);
@@ -3018,16 +3050,6 @@ bool check_type_internal(Checker *c, AstNode *e, Type **type, Type *named_type)
 		return true;
 	case_end;
 
-/* 	case_ast_node(rut, RawUnionType, e);
-		*type = make_type_raw_union(c->allocator);
-		set_base_type(named_type, *type);
-		check_open_scope(c, e);
-		check_raw_union_type(c, *type, e);
-		check_close_scope(c);
-		(*type)->Struct.node = e;
-		return true;
-	case_end;
- */
 	case_ast_node(et, EnumType, e);
 		*type = make_type_enum(c->allocator);
 		set_base_type(named_type, *type);
@@ -4815,7 +4837,7 @@ bool check_builtin_procedure(Checker *c, Operand *operand, AstNode *call, i32 id
 
 	bool vari_expand = (ce->ellipsis.pos.line != 0);
 	// if (vari_expand && id != BuiltinProc_append) {
-		// error(ce->ellipsis, "Invalid use of `..` with built-in procedure `append`");
+		// error(ce->ellipsis, "Invalid use of `...` with built-in procedure `append`");
 		// return false;
 	// }
 
@@ -5914,6 +5936,7 @@ int valid_proc_and_score_cmp(void const *a, void const *b) {
 	return sj < si ? -1 : sj > si;
 }
 
+
 bool check_unpack_arguments(Checker *c, isize lhs_count, Array<Operand> *operands, Array<AstNode *> rhs, bool allow_ok) {
 	bool optional_ok = false;
 	for_array(i, rhs) {
@@ -6009,14 +6032,14 @@ CALL_ARGUMENT_CHECKER(check_call_arguments_internal) {
 	if (vari_expand && !variadic) {
 		if (show_error) {
 			error(ce->ellipsis,
-			      "Cannot use `..` in call to a non-variadic procedure: `%.*s`",
+			      "Cannot use `...` in call to a non-variadic procedure: `%.*s`",
 			      LIT(ce->proc->Ident.token.string));
 		}
 		err = CallArgumentError_NonVariadicExpand;
 	} else if (vari_expand && pt->c_vararg) {
 		if (show_error) {
 			error(ce->ellipsis,
-			      "Cannot use `..` in call to a `#c_vararg` variadic procedure: `%.*s`",
+			      "Cannot use `...` in call to a `#c_vararg` variadic procedure: `%.*s`",
 			      LIT(ce->proc->Ident.token.string));
 		}
 		err = CallArgumentError_NonVariadicExpand;
@@ -6110,7 +6133,7 @@ CALL_ARGUMENT_CHECKER(check_call_arguments_internal) {
 						t = slice;
 						if (operand_index != param_count) {
 							if (show_error) {
-								error(o.expr, "`..` in a variadic procedure can only have one variadic argument at the end");
+								error(o.expr, "`...` in a variadic procedure can only have one variadic argument at the end");
 							}
 							if (data) {
 								data->score = score;
@@ -6130,15 +6153,6 @@ CALL_ARGUMENT_CHECKER(check_call_arguments_internal) {
 					score += s;
 				}
 			}
-
-			if (gen_entity != nullptr && gen_entity->token.string == "append" && err != CallArgumentError_None) {
-				gb_printf_err("append %s with score %lld %d\n", type_to_string(final_proc_type), score, err);
-			}
-
-			if (err == CallArgumentError_None && poly_proc_data.proc_info.decl != nullptr) {
-				// NOTE(bill): Check the newly generated procedure body
-				check_procedure_later(c, poly_proc_data.proc_info);
-			}
 		}
 	}
 
@@ -6281,9 +6295,6 @@ CALL_ARGUMENT_CHECKER(check_named_call_arguments) {
 		PolyProcData poly_proc_data = {};
 		if (find_or_generate_polymorphic_procedure_from_parameters(c, entity, &ordered_operands, &poly_proc_data)) {
 			gen_entity = poly_proc_data.gen_entity;
-			if (poly_proc_data.proc_info.decl != nullptr) {
-				check_procedure_later(c, poly_proc_data.proc_info);
-			}
 			Type *gept = base_type(gen_entity->type);
 			GB_ASSERT(is_type_proc(gept));
 			pt = &gept->Proc;
@@ -6354,7 +6365,7 @@ CallArgumentData check_call_arguments(Checker *c, Operand *operand, Type *proc_t
 
 		bool vari_expand = (ce->ellipsis.pos.line != 0);
 		if (vari_expand) {
-			// error(ce->ellipsis, "Invalid use of `..` with `field = value` call`");
+			// error(ce->ellipsis, "Invalid use of `...` with `field = value` call`");
 		}
 
 	} else {
@@ -6594,7 +6605,7 @@ CallArgumentError check_polymorphic_struct_type(Checker *c, Operand *operand, As
 
 		bool vari_expand = (ce->ellipsis.pos.line != 0);
 		if (vari_expand) {
-			error(ce->ellipsis, "Invalid use of `..` in a polymorphic type call`");
+			error(ce->ellipsis, "Invalid use of `...` in a polymorphic type call`");
 		}
 
 	} else {
@@ -7735,9 +7746,13 @@ ExprKind check_expr_base_internal(Checker *c, Operand *o, AstNode *node, Type *t
 			if (!ok) {
 				gbString expr_str = expr_to_string(o->expr);
 				gbString dst_type_str = type_to_string(t);
-				error(o->expr, "Cannot type assert `%s` to `%s` as it is not a variant of that union", expr_str, dst_type_str);
-				gb_string_free(dst_type_str);
-				gb_string_free(expr_str);
+				defer (gb_string_free(expr_str));
+				defer (gb_string_free(dst_type_str));
+				if (bsrc->Union.variants.count == 0) {
+					error(o->expr, "Cannot type assert `%s` to `%s` as this is an empty union", expr_str, dst_type_str);
+				} else {
+					error(o->expr, "Cannot type assert `%s` to `%s` as it is not a variant of that union", expr_str, dst_type_str);
+				}
 				o->mode = Addressing_Invalid;
 				o->expr = node;
 				return kind;
@@ -8021,7 +8036,7 @@ ExprKind check_expr_base_internal(Checker *c, Operand *o, AstNode *node, Type *t
 			return kind;
 		} else {
 			Type *t = base_type(o->type);
-			if (t->kind == Type_Pointer) {
+			if (t->kind == Type_Pointer && !is_type_empty_union(t->Pointer.elem)) {
 				if (o->mode != Addressing_Immutable) {
 					o->mode = Addressing_Variable;
 				}
@@ -8315,7 +8330,7 @@ gbString write_expr_to_string(gbString str, AstNode *node) {
 		if (at->count != nullptr &&
 		    at->count->kind == AstNode_UnaryExpr &&
 		    at->count->UnaryExpr.op.kind == Token_Ellipsis) {
-			str = gb_string_appendc(str, "..");
+			str = gb_string_appendc(str, "...");
 		} else {
 			str = write_expr_to_string(str, at->count);
 		}
diff --git a/src/check_stmt.cpp b/src/check_stmt.cpp
index a55e74350..189bff7fd 100644
--- a/src/check_stmt.cpp
+++ b/src/check_stmt.cpp
@@ -1733,6 +1733,11 @@ void check_stmt_internal(Checker *c, AstNode *node, u32 flags) {
 				error(vd->type, "Invalid use of a polymorphic type `%s` in variable declaration", str);
 				gb_string_free(str);
 				init_type = t_invalid;
+			} else if (is_type_empty_union(init_type)) {
+				gbString str = type_to_string(init_type);
+				error(vd->type, "An empty union `%s` cannot be instantiated in variable declaration", str);
+				gb_string_free(str);
+				init_type = t_invalid;
 			}
 		}
 
diff --git a/src/checker.cpp b/src/checker.cpp
index 0f628a84a..4c77f25ee 100644
--- a/src/checker.cpp
+++ b/src/checker.cpp
@@ -185,7 +185,7 @@ struct DeclInfo {
 
 	AstNode *         type_expr;
 	AstNode *         init_expr;
-	AstNode *         proc_lit; // AstNode_ProcLit
+	AstNode *         proc_lit;      // AstNode_ProcLit
 	Type *            gen_proc_type; // Precalculated
 
 	Map<bool>         deps; // Key: Entity *
diff --git a/src/entity.cpp b/src/entity.cpp
index d2c29ca98..21ef9095f 100644
--- a/src/entity.cpp
+++ b/src/entity.cpp
@@ -98,6 +98,7 @@ struct Entity {
 		} Variable;
 		struct {
 			bool is_type_alias;
+			Type *type_parameter_specialization;
 		} TypeName;
 		struct {
 			OverloadKind overload_kind;
diff --git a/src/ir_print.cpp b/src/ir_print.cpp
index 78090e6ac..23c385140 100644
--- a/src/ir_print.cpp
+++ b/src/ir_print.cpp
@@ -282,21 +282,20 @@ void ir_print_type(irFileBuffer *f, irModule *m, Type *t) {
 		return;
 
 	case Type_Union: {
-		// NOTE(bill): The zero size array is used to fix the alignment used in a structure as
-		// LLVM takes the first element's alignment as the entire alignment (like C)
-		i64 align = type_align_of(heap_allocator(), t);
-		i64 total_size = type_size_of(heap_allocator(), t);
-	#if 1
-		i64 block_size =  t->Union.variant_block_size;
+		if (t->Union.variants.count == 0) {
+			ir_fprintf(f, "%%..opaque");
+		} else {
+			// NOTE(bill): The zero size array is used to fix the alignment used in a structure as
+			// LLVM takes the first element's alignment as the entire alignment (like C)
+			i64 align = type_align_of(heap_allocator(), t);
+			i64 total_size = type_size_of(heap_allocator(), t);
+			i64 block_size =  t->Union.variant_block_size;
 
-		ir_fprintf(f, "{[0 x <%lld x i8>], ", align);
-		ir_fprintf(f, "[%lld x i8], ", block_size);
-		ir_print_type(f, m, t_type_info_ptr);
-		ir_fprintf(f, "}");
-	#else
-		i64 block_size = total_size - build_context.word_size;
-		ir_fprintf(f, "{[0 x <%lld x i8>], [%lld x i8], i%lld}", align, block_size, word_bits);
-	#endif
+			ir_fprintf(f, "{[0 x <%lld x i8>], ", align);
+			ir_fprintf(f, "[%lld x i8], ", block_size);
+			ir_print_type(f, m, t_type_info_ptr);
+			ir_fprintf(f, "}");
+		}
 	} return;
 
 	case Type_Struct: {
@@ -1733,6 +1732,8 @@ void print_llvm_ir(irGen *ir) {
 	irFileBuffer buf = {}, *f = &buf;
 	ir_file_buffer_init(f, &ir->output_file);
 
+	ir_print_encoded_local(f, str_lit("..opaque"));
+	ir_fprintf(f, " = type opaque;\n");
 	ir_print_encoded_local(f, str_lit("..string"));
 	ir_fprintf(f, " = type {i8*, ");
 	ir_print_type(f, m, t_int);
diff --git a/src/parser.cpp b/src/parser.cpp
index 21f3e3df4..9b848ca7e 100644
--- a/src/parser.cpp
+++ b/src/parser.cpp
@@ -633,7 +633,8 @@ AstNode *clone_ast_node(gbAllocator a, AstNode *node) {
 	case AstNode_BasicDirective: break;
 
 	case AstNode_PolyType:
-		n->PolyType.type = clone_ast_node(a, n->PolyType.type);
+		n->PolyType.type           = clone_ast_node(a, n->PolyType.type);
+		n->PolyType.specialization = clone_ast_node(a, n->PolyType.specialization);
 		break;
 	case AstNode_Ellipsis:
 		n->Ellipsis.expr = clone_ast_node(a, n->Ellipsis.expr);
@@ -833,6 +834,7 @@ AstNode *clone_ast_node(gbAllocator a, AstNode *node) {
 		break;
 
 	case AstNode_TypeType:
+		n->TypeType.specialization = clone_ast_node(a, n->TypeType.specialization);
 		break;
 	case AstNode_HelperType:
 		n->HelperType.type = clone_ast_node(a, n->HelperType.type);
diff --git a/src/types.cpp b/src/types.cpp
index 360b9ed15..e7f183e79 100644
--- a/src/types.cpp
+++ b/src/types.cpp
@@ -146,6 +146,7 @@ struct TypeStruct {
 		bool     c_vararg;                                \
 		bool     is_polymorphic;                          \
 		bool     is_poly_specialized;                     \
+		isize    specialization_count;                    \
 		ProcCallingConvention calling_convention;         \
 	})                                                    \
 	TYPE_KIND(Map, struct {                               \
@@ -873,6 +874,11 @@ bool is_type_untyped_undef(Type *t) {
 }
 
 
+bool is_type_empty_union(Type *t) {
+	t = base_type(t);
+	return t->kind == Type_Union && t->Union.variants.count == 0;
+}
+
 
 bool is_type_valid_for_keys(Type *t) {
 	t = core_type(t);
@@ -1822,6 +1828,9 @@ i64 type_align_of_internal(gbAllocator allocator, Type *t, TypePath *path) {
 		return type_align_of_internal(allocator, t->Enum.base_type, path);
 
 	case Type_Union: {
+		if (t->Union.variants.count == 0) {
+			return 1;
+		}
 		i64 max = build_context.word_size;
 		for_array(i, t->Union.variants) {
 			Type *variant = t->Union.variants[i];
@@ -2056,6 +2065,9 @@ i64 type_size_of_internal(gbAllocator allocator, Type *t, TypePath *path) {
 		return type_size_of_internal(allocator, t->Enum.base_type, path);
 
 	case Type_Union: {
+		if (t->Union.variants.count == 0) {
+			return 0;
+		}
 		i64 align = type_align_of_internal(allocator, t, path);
 		if (path->failure) {
 			return FAILURE_SIZE;
@@ -2294,7 +2306,7 @@ gbString write_type_to_string(gbString str, Type *type) {
 		break;
 
 	case Type_Union:
-		str = gb_string_appendc(str, "union{");
+		str = gb_string_appendc(str, "union {");
 		for_array(i, type->Union.variants) {
 			Type *t = type->Union.variants[i];
 			if (i > 0) str = gb_string_appendc(str, ", ");
@@ -2304,40 +2316,22 @@ gbString write_type_to_string(gbString str, Type *type) {
 		break;
 
 	case Type_Struct: {
-		if (type->Struct.is_raw_union) {
-			str = gb_string_appendc(str, "raw_union{");
-			for_array(i, type->Struct.fields) {
-				Entity *f = type->Struct.fields[i];
-				GB_ASSERT(f->kind == Entity_Variable);
-				if (i > 0) {
-					str = gb_string_appendc(str, ", ");
-				}
-				str = gb_string_append_length(str, f->token.string.text, f->token.string.len);
-				str = gb_string_appendc(str, ": ");
-				str = write_type_to_string(str, f->type);
-			}
-			str = gb_string_appendc(str, "}");
-		} else {
 			str = gb_string_appendc(str, "struct");
-			if (type->Struct.is_packed) {
-				str = gb_string_appendc(str, " #packed");
-			}
-			if (type->Struct.is_ordered) {
-				str = gb_string_appendc(str, " #ordered");
-			}
-			str = gb_string_appendc(str, " {");
-			for_array(i, type->Struct.fields) {
-				Entity *f = type->Struct.fields[i];
-				GB_ASSERT(f->kind == Entity_Variable);
-				if (i > 0) {
-					str = gb_string_appendc(str, ", ");
-				}
-				str = gb_string_append_length(str, f->token.string.text, f->token.string.len);
-				str = gb_string_appendc(str, ": ");
-				str = write_type_to_string(str, f->type);
+		if (type->Struct.is_packed)    str = gb_string_appendc(str, " #packed");
+		if (type->Struct.is_ordered)   str = gb_string_appendc(str, " #ordered");
+		if (type->Struct.is_raw_union) str = gb_string_appendc(str, " #raw_union");
+		str = gb_string_appendc(str, " {");
+		for_array(i, type->Struct.fields) {
+			Entity *f = type->Struct.fields[i];
+			GB_ASSERT(f->kind == Entity_Variable);
+			if (i > 0) {
+				str = gb_string_appendc(str, ", ");
 			}
-			str = gb_string_appendc(str, "}");
+			str = gb_string_append_length(str, f->token.string.text, f->token.string.len);
+			str = gb_string_appendc(str, ": ");
+			str = write_type_to_string(str, f->type);
 		}
+		str = gb_string_appendc(str, "}");
 	} break;
 
 	case Type_Map: {
@@ -2373,7 +2367,7 @@ gbString write_type_to_string(gbString str, Type *type) {
 						}
 						if (var->flags&EntityFlag_Ellipsis) {
 							Type *slice = base_type(var->type);
-							str = gb_string_appendc(str, "..");
+							str = gb_string_appendc(str, "...");
 							GB_ASSERT(var->type->kind == Type_Slice);
 							str = write_type_to_string(str, slice->Slice.elem);
 						} else {