[Version 9.0] Feature support for target typed new

standard/conversions.md

@@ -25,7 +25,7 @@
 > ```csharp
 > enum Color { Red, Blue, Green }
 >
 > // The expression 0 converts implicitly to enum types
 > Color c0 = 0;
 >
 > // Other int expressions need explicit conversion
@@ -390,6 +390,12 @@
 
 There is an implicit conversion from a *switch_expression* ([§12.11](expressions.md#1211-switch-expression)) to every type `T` for which there exists an implicit conversion from each *switch_expression_arm*’s *switch_expression_arm_expression*’s to `T`.
 
+### §imp-obj-creation-conv Implicit object-creation conversions
+
+There is an implicit ***object-creation conversion*** from a *target_typed_new* expression ([§12.8.17.2](expressions.md#128172-object-creation-expressions)) to every type.
+
+Given a target type `T`, if `T` is an instance of `System.Nullable`, the type `T0` is `T`'s underlying type. Otherwise `T0` is `T`. The meaning of a *target_typed_new* expression that is converted to the type `T` is the same as the meaning of a corresponding *object_creation_expression* that specifies `T0` as the type.
+
 ## 10.3 Explicit conversions
 
 ### 10.3.1 General

standard/expressions.md

@@ -1,15 +1,15 @@
 # 12 Expressions
 
 ## 12.1 General
 
 An expression is a sequence of operators and operands. This clause defines the syntax, order of evaluation of operands and operators, and meaning of expressions.
 
 ## 12.2 Expression classifications
 
 ### 12.2.1 General
 
 The result of an expression is classified as one of the following:
 
 - A value. Every value has an associated type.
 - A variable. Unless otherwise specified, a variable is explicitly typed and has an associated type, namely the declared type of the variable. An implicitly typed variable has no associated type.
 - A null literal. An expression with this classification can be implicitly converted to a reference type or nullable value type.
@@ -2526,6 +2526,11 @@
 object_creation_expression
     : 'new' type '(' argument_list? ')' object_or_collection_initializer?
     | 'new' type object_or_collection_initializer
+    | target_typed_new
+    ;
+
+target_typed_new
+    : 'new' '(' argument_list? ')' object_or_collection_initializer?
     ;
 
 object_or_collection_initializer
@@ -2536,6 +2541,10 @@
 
 The *type* of an *object_creation_expression* shall be a *class_type*, a *value_type*, or a *type_parameter*. The *type* cannot be a *tuple_type* or an abstract or static *class_type*.
 
+If `type` can be inferred from usage, it can be omitted, as allowed by *target_typed_new*. It is a compile-time error to omit `type` if the type cannot be inferred. A *target_typed_new* expression has no type. However, there is an implicit object-creation conversion (§imp-obj-creation-conv) from a *target_typed_new* expression to every type. It is a compile-time error if a *target_typed_new* is used as an operand of a unary or binary operator, or if it is used where it is not subject to an object-creation conversion.
+
+If `type` is present, let `T` be that type; otherwise, let `T` be the implied type.
+
 The optional *argument_list* ([§12.6.2](expressions.md#1262-argument-lists)) is permitted only if the *type* is a *class_type* or a *struct_type*.
 
 An object creation expression can omit the constructor argument list and enclosing parentheses provided it includes an object initializer or collection initializer. Omitting the constructor argument list and enclosing parentheses is equivalent to specifying an empty argument list.
@@ -2544,7 +2553,7 @@
 
 If any of the arguments in the optional *argument_list* has the compile-time type `dynamic` then the *object_creation_expression* is dynamically bound ([§12.3.3](expressions.md#1233-dynamic-binding)) and the following rules are applied at run-time using the run-time type of those arguments of the *argument_list* that have the compile-time type `dynamic`. However, the object creation undergoes a limited compile-time check as described in [§12.6.5](expressions.md#1265-compile-time-checking-of-dynamic-member-invocation).
 
-The binding-time processing of an *object_creation_expression* of the form `new T(A)`, where `T` is a *class_type*, or a *value_type*, and `A` is an optional *argument_list*, consists of the following steps:
+The binding-time processing of an *object_creation_expression* of the form `new T(A)`, where the specified or implied type `T` is a *class_type*, or a *value_type*, and `A` is an optional *argument_list*, consists of the following steps:
 
 - If `T` is a *value_type* and `A` is not present:
   - The *object_creation_expression* is a default constructor invocation. The result of the *object_creation_expression* is a value of type `T`, namely the default value for `T` as defined in [§8.3.3](types.md#833-default-constructors).
@@ -2559,7 +2568,7 @@
 
 Even if the *object_creation_expression* is dynamically bound, the compile-time type is still `T`.
 
-The run-time processing of an *object_creation_expression* of the form new `T(A)`, where `T` is *class_type* or a *struct_type* and `A` is an optional *argument_list*, consists of the following steps:
+The run-time processing of an *object_creation_expression* of the form `new T(A)`, where the specified or implied type `T` is *class_type* or a *struct_type* and `A` is an optional *argument_list*, consists of the following steps:
 
 - If `T` is a *class_type*:
   - A new instance of class `T` is allocated. If there is not enough memory available to allocate the new instance, a `System.OutOfMemoryException` is thrown and no further steps are executed.

standard/statements.md

@@ -1739,7 +1739,7 @@ throw_statement
     ;
 ```
 
-A `throw` statement with an expression throws an exception produced by evaluating the expression. The expression shall be implicitly convertible to `System.Exception`, and the result of evaluating the expression is converted to `System.Exception` before being thrown. If the result of the conversion is `null`, a `System.NullReferenceException` is thrown instead.
+A `throw` statement with an expression throws an exception produced by evaluating the expression. The expression shall be implicitly convertible to `System.Exception`, and the result of evaluating the expression is converted to `System.Exception` before being thrown. If *expression* is a *target_typed_new* expression ([§12.8.17.2](expressions.md#128172-object-creation-expressions)), the target type is `System.Exception`. If the result of the conversion is `null`, a `System.NullReferenceException` is thrown instead.
 
 A `throw` statement with no expression can be used only in a `catch` block, in which case, that statement re-throws the exception that is currently being handled by that `catch` block.