We need to talk about error messages of functions that are passed into other functions at compile time

[Seb via Digitalmars-d]

On Saturday, 28 May 2016 at 13:37:55 UTC, maik klein wrote:
> I really like D's syntax for lambdas and I usually write code 
> like this
>
>   auto v = validationLayers[].all!((layerName){
>     return layerProps[].count!((layer){
>       return strcmp(cast(const(char*))layer.layerName, 
> layerName) == 0;
>     }) > 0;
>   });
>
> But this gives you basically 0 helpful error messages:
>
>
> "Error: template 
> breeze.graphics.context.createContext.all!((layerName)
> {
> return layerProps[].count!((layer)
> {
> return strcmp(cast(const(char*))layer.layerName, layerName) == 
> 0;
> }
> ) > 0;
> }
> ).all cannot deduce function from argument types 
> !()(const(char*)[]), candidates are:
> /usr/include/dmd/phobos/std/algorithm/searching.d(113,10):
>   breeze.graphics.context.createContext.all!((layerName)
> {
> return layerProps[].count!((layer)
> {
> return strcmp(cast(const(char*))layer.layerName, layerName) == 
> 0;
> }
> ) > 0;
> }
> ).all(Range)(Range range) if (isInputRange!Range && 
> is(typeof(unaryFun!pred(range.front))))
> dmd failed with exit code 1"
>
> For example I simply forgot to import `count`, nothing in the 
> error message is really helpful and the only way to know for 
> sure is to rip the function apart, which is not a very fun 
> thing to do.
>
> You can't also rip it apart easily because in the case above I 
> implicitly capture `layerName` in the closure for `count`.
>
> What are you thoughts on this?

You are not the first who complains - the issue tracker [1] is 
full with issues about bad error messages

https://issues.dlang.org/show_bug.cgi?id=15893
https://issues.dlang.org/show_bug.cgi?id=15614
https://issues.dlang.org/show_bug.cgi?id=15597
https://issues.dlang.org/show_bug.cgi?id=15215
...

On the recent Slant about Programming languages [2] "Error 
messages can be confusing, especially for newcomers" was the 
highest up-voted Con of D.

[1] 
https://issues.dlang.org/buglist.cgi?quicksearch=error%20messages&list_id=208649
[2] 
http://www.slant.co/topics/5984/~productivity-enhancing-well-designed-and-concise-rather-than-just-popular-or-time-tested-programming-la