DIP23

DIP23: Fixing properties redux

Title:	Fixing properties
DIP:	23
Version:	1
Status:	Draft
Created:	2013-02-02
Last Modified:	2013-02-02
Author:	Andrei Alexandrescu and Walter Bright
Links:

Abstract

There has been significant debate about finalizing property implementation. This document attempts to provide a proposal of reasonable complexity along with checkable examples.

Forces:

• Break as little code as possible
• Avoid departing from the existing and intended syntax and semantics of properties
• Make economy of means (little or no new syntax to learn)
• Avoid embarrassing situations such as expressions with unexpressible types or no-op address-of operator (as is the case with C functions).

Rationale

goes here

Description

Optional parens stay in

One can't discuss properties without also discussing optional parens. These obviate to some extent the need for properties (at least of the read-only kind) and make for potential ambiguities.

This proposal sustains that optional parentheses should stay in. That means, if a function or method may be called without arguments, the trailing parens may be omitted.

unittest
{
    int a;
    void fun1() { ++a; }
    // will call fun
    fun1;
    assert(a == 1);

    // Works with default arguments, too
    void fun2(string s = "abc") { ++a; }
    fun2;
    assert(a == 2);
}

The same goes about methods:

unittest
{
    int a;
    struct S1 { void fun1() { ++a; } }
    S1 s1;
    // will call fun
    s1.fun1;
    assert(a == 1);

    // Works with default arguments, too
    struct S2 { void fun2(string s = "abc") { ++a; } }
    S2 s2;
    s2.fun2;
    assert(a == 2);
}

However, that's not the case with function objects, delegate objects, or objects that implement the function call operator.

unittest
{
    static int a;
    static void fun1() { ++a; }
    auto p1 = &fun1;
    // Error: var has no effect in expression (p1)
    p1;
    assert(a == 0);
}
unittest
{
    int a;
    void fun1() { ++a; }
    auto p1 = &fun1;
    // Error: var has no effect in expression (p1)
    p1;
    assert(a == 0);
}
unittest
{
    static int a;
    struct S1 { void opCall() { ++a; } }
    S1 s1;
    // Error: var has no effect in expression (s1)    s1;
    assert(a == 0);
}

Talk

goes here

Copyright

This document has been placed in the Public Domain.