• via Digitalmars-d-bugs (42/42) Mar 09 2016 https://issues.dlang.org/show_bug.cgi?id=15781

via Digitalmars-d-bugs <digitalmars-d-bugs puremagic.com> writes:

https://issues.dlang.org/show_bug.cgi?id=15781

          Issue ID: 15781
           Summary: Type deduction const
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: regression
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: jbc.engelen gmail.com

```
struct TypeA {
    int value;
}

auto foo(T)(T start, T end) {
   import std.stdio;
   writeln(typeid(T));
}


void main() {
    alias Tiep = TypeA;
    const Tiep a;
    Tiep b;

    Tiep c = a;  // This is fine
    foo(c,b);

    foo(a,b);    // This is not fine with DMD 2.069.2
}
```

The code compiles fine with DMD 2.068.2.
The code fails to compile with DMD 2.068.2 and DMD 2.070.2:
deduce.d(19): Error: template deduce.foo cannot deduce function from argument
types !()(const(TypeA), TypeA), candidates are:
deduce.d(5):        deduce.foo(T)(T start, T end)

I believe this is a regression.
DMD 2.068.2 deduces T = TypeA (non-const).

For `alias Tiep = int;` it compiles with DMD 2.070.2.
Also when modifying the code to read `auto foo(T)(const T start, const T end)`.

This issue was reported after a brief forum discussion:
http://forum.dlang.org/thread/pviqlkktqzeusjualhuk forum.dlang.org.

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