[Issue 10491] Type inference for function arguments with default value

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=10491



--- Comment #2 from Kenji Hara <k.hara.pg at gmail.com> 2013-06-28 21:13:50 PDT ---
I don't like the enhancements of this kind. Because:

1. Default argument is not so often used. Then, reduction amount of the code is
very limited.
2. It breaks consistency of C-style languages that all of function parameters
in function signature have their own type explicitly.
3. It would introduce one more forward reference possibility.

void foo(auto a = bar()) {}   // inference

auto bar()
{
    alias T = ParameterTypeTuple!foo[0];   // requires foo's complete signature
    return T.init;
}

void main()
{
    auto x = bar();
}

Already, auto return, function attribute inference has same possibility. They
sometimes produces legitimate (but difficult to understand) forward reference
errors.

4. `auto ref` / `in ref` is still debatable. This enhancement might have
interference with it. 

----

Side note: Today, issue 7152 is implemented. By that,

void foo(in VeryLongNamedStruct x = VeryLongNamedStruct(1)) {}

might be shorten to:

void foo(in VeryLongNamedStruct x = 1) {}

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