DIP10005: Dependency-Carrying Declarations is now available for community feedback

[default0 via Digitalmars-d]

On Wednesday, 14 December 2016 at 14:21:55 UTC, Andrei 
Alexandrescu wrote:
> On 12/14/16 8:26 AM, Dominikus Dittes Scherkl wrote:
>> On Tuesday, 13 December 2016 at 22:33:24 UTC, Andrei 
>> Alexandrescu wrote:
>>> Destroy.
>>>
>>> https://github.com/dlang/DIPs/pull/51/files
>>
>> Why not leave it as it is and only change the compiler to
>> perform inputs _within_ a function before evaluating the 
>> declaration, so
>> that the symbols imported can be used in the declaration?
>
> Thanks. I considered this but it put pressure on the 
> relationship between the name and where it's looked up. 
> Consider that imports in a function don't need to be at the 
> top. They may also be in nested scopes inside the function. It 
> becomes quite tenuous to explain where the parameter type names 
> are looked up. -- Andrei

Could restrict to imports that come before any other statements 
in the function body, ie:

// valid, compiles when instantiated
void fun(Range)(Range r) if(isInputRange!Range) {
     import std.range;
}

// invalid, import is not picked up because it is not the first 
statement in the method body
void fun(Range)(Range r) if(isInputRange!Range) {
     doThings();
     import std.range;
}

If this is desirable, the error message for failed symbol lookup 
of symbols in a function declaration should hint that imports in 
the function body are only considered if they stand at the 
beginning of the function, to help mitigate confusion.
Seems simple enough to specify and explain, honestly.