• Mathias Lang (36/36) Jun 25 2015 Hi everyone,
• Atila Neves (6/11) Jun 25 2015 This is part of a bigger issue involving error messages for

"Mathias Lang" <pro.mathias.lang gmail.com> writes:

Hi everyone,
I've been doing quite a lot of range-based code lately and I've 
been bugged with an UX problem that's IMHO a real bummer for 
range usage to new users.

Take the example code:
```
import std.algorithm;
void main()
{
     auto foo = [ "foo": "foo", "bar": "bar", "foobar": "foobar" ];
     assert(foo.byKeyValue.all!((kvp) => kvp.Key == kvp.Value));
}
```

Quite straightforward, right ? Some of you might already have 
spotted the error, but here's what DMD think of it:

```
test.d(6): Error: template std.algorithm.searching.all cannot 
deduce function from argument types !((kvp) => kvp.Key == 
kvp.Value)(Result), candidates are:
/dlang/dmd-2.067.0/linux/bin64/../../src/phobos/std/algorithm/searching.d(100):
       std.algorithm.searching.all(alias pred = "a")

```

This happens because I got the delegate wrong. To get the right 
error, you have to know errors are gagged and so, let's remove 
the type inference error:

```
assert(foo.byKeyValue.all!((typeof(foo.byKeyValue.front) kvp) => 
kvp.Key == kvp.Value));
```

Which gives a proper error message:

```
test.d(6): Error: no property 'Key' for type 'Pair', did you mean 
'key'?
test.d(6): Error: no property 'Value' for type 'Pair', did you 
mean 'value'?
```

Any change we can fix that ?

"Atila Neves" <atila.neves gmail.com> writes:

On Thursday, 25 June 2015 at 13:27:23 UTC, Mathias Lang wrote:
 Hi everyone,
 I've been doing quite a lot of range-based code lately and I've 
 been bugged with an UX problem that's IMHO a real bummer for 
 range usage to new users.

 [...]


This is part of a bigger issue involving error messages for 
compilation errors due to not implementing a compile-interface 
such as InputRange. I've been meaning to write a DIP for this for 
a year now, I just need to find the time.

Atila