Add 'instantiate<T>' builtin (like 'new' but from a type), see #349

src/builtins.ts

@@ -2322,6 +2322,25 @@ export function compileCall(
       // thus must be used with care. it exists because it *might* be useful in specific scenarios.
       return module.createCallIndirect(arg0, operandExprs, typeName);
     }
+    case "instantiate": {
+      if (!(typeArguments && typeArguments.length == 1)) {
+        if (typeArguments && typeArguments.length) compiler.currentType = typeArguments[0];
+        compiler.error(
+          DiagnosticCode.Expected_0_type_arguments_but_got_1,
+          reportNode.range, "1", typeArguments ? typeArguments.length.toString(10) : "0"
+        );
+        return module.createUnreachable();
+      }
+      let classInstance = typeArguments[0].classReference;
+      if (!classInstance) {
+        compiler.error(
+          DiagnosticCode.Operation_not_supported,
+          reportNode.range
+        );
+        return module.createUnreachable();
+      }
+      return compiler.compileInstantiate(classInstance, operands, reportNode);
+    }
 
     // user-defined diagnostic macros
 

src/compiler.ts

@@ -6651,9 +6651,10 @@ export class Compiler extends DiagnosticEmitter {
       );
     }
     if (!classInstance) return module.createUnreachable();
+    return this.compileInstantiate(classInstance, expression.arguments, expression);
+  }
 
-    var expr: ExpressionRef;
-
+  compileInstantiate(classInstance: Class, argumentExpressions: Expression[], reportNode: Node): ExpressionRef {
     // traverse to the top-most visible constructor
     var currentClassInstance: Class | null = classInstance;
     var constructorInstance: Function | null = null;
@@ -6663,14 +6664,21 @@ export class Compiler extends DiagnosticEmitter {
     } while (currentClassInstance = currentClassInstance.base);
 
     // if a constructor is present, call it with a zero `this`
+    var expr: ExpressionRef;
     if (constructorInstance) {
-      expr = this.compileCallDirect(constructorInstance, expression.arguments, expression,
-        options.usizeType.toNativeZero(module)
+      expr = this.compileCallDirect(constructorInstance, argumentExpressions, reportNode,
+        this.options.usizeType.toNativeZero(this.module)
       );
 
     // otherwise simply allocate a new instance and initialize its fields
     } else {
-      expr = this.makeAllocate(classInstance, expression);
+      if (argumentExpressions.length) {
+        this.error(
+          DiagnosticCode.Expected_0_arguments_but_got_1,
+          reportNode.range, "0", argumentExpressions.length.toString(10)
+        );
+      }
+      expr = this.makeAllocate(classInstance, reportNode);
     }
 
     this.currentType = classInstance.type;

std/assembly/builtins.ts

@@ -41,6 +41,7 @@
 @builtin export declare function assert<T>(isTrueish: T, message?: string): T;
 @builtin export declare function unchecked<T>(expr: T): T;
 @builtin export declare function call_indirect<T>(target: void, ...args: void[]): T;
+@builtin export declare function instantiate<T>(...args: void[]): T;
 
 @builtin export declare function i8(value: void): i8;
 export namespace i8 {

std/assembly/index.d.ts

@@ -112,6 +112,8 @@ declare function changetype<T>(value: any): T;
 declare function unchecked<T>(value: T): T;
 /** Emits a `call_indirect` instruction, calling the specified function in the function table by index with the specified arguments. Does result in a runtime error if the arguments do not match the called function. */
 declare function call_indirect<T>(target: Function | u32, ...args: any[]): T;
+/** Instantiates a new instance of `T` using the specified constructor arguments. */
+declare function instantiate<T>(...args: any[]): T;
 /** Tests if a 32-bit or 64-bit float is `NaN`. */
 declare function isNaN<T = f32 | f64>(value: T): bool;
 /** Tests if a 32-bit or 64-bit float is finite, that is not `NaN` or +/-`Infinity`. */