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digitalmars.D - We need to talk about error messages of functions that are passed into

reply maik klein <maikklein googlemail.com> writes:
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?
May 28 2016
parent Seb <seb wilzba.ch> writes:
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
May 28 2016