what's the point of function template declarations if they can't be defined?

[Timothee Cour]

> It's been my understanding that it's always been illegal to provide a
definition for a function that was declared previously unless it was
declared in a .di file

Compiler has always allowed that:
```
void fun();
void fun(){}
```
(but see details in bug report)

> It's useful with stuff like version(Ddoc).

I guess you mean `version(StdDdoc)` ?

On that note, I see things like this, which are not DRY:
```
version(StdDdoc) string readLink(R)(R link)
if (isInputRange!R && !isInfinite!R && isSomeChar!(ElementEncodingType!R) ||
    isConvertibleToString!R);
else version(Posix) string readLink(R)(R link)
if (isInputRange!R && !isInfinite!R && isSomeChar!(ElementEncodingType!R) ||
    isConvertibleToString!R)
 ```

Is this pattern used because we want to build DDoc on a
not-necessarily Posix system (ie to get a DDoc regardless of which
environment)?

If so, it seems like an anti-pattern; better options could be:
* build platform specific documentation (which actually makes sense,
eg a windows user may not want to see Posix-only functions)
* add a special compiler flag that overrides predefined builtins (eg Posix)



On Wed, Feb 7, 2018 at 11:21 PM, Jonathan M Davis via
Digitalmars-d-learn <digitalmars-d-learn at puremagic.com> wrote:
> On Wednesday, February 07, 2018 13:39:55 Timothee Cour via Digitalmars-d-
> learn wrote:
>> ```
>> void fun_bad3(T)(T a);  // declaration [1]
>> void fun_bad3(T)(T a){};  // definition [2]
>> void test(){
>>   fun_bad3(1);
>> }
>> ```
>> Error: test_all.fun_bad3 called with argument types (int) matches both:
>> main.d(11):     test_all.fun_bad3!int.fun_bad3(int a)
>> and:
>> main.d(12):     test_all.fun_bad3!int.fun_bad3(int a)
>>
>> should [1] be allowed?
>
> It's useful with stuff like version(Ddoc).
>
>> compler doens't allow defining it afterwards in
>> [2] (unlike function definitions, and, well, modulo this regression
>> https://issues.dlang.org/show_bug.cgi?id=18393)
>
> It's been my understanding that it's always been illegal to provide a
> definition for a function that was declared previously unless it was
> declared in a .di file, in which case, you're not really both declaring and
> defining it, but the .d file is used when the module is compiled, and the
> .di file is used by other modules which use that module, so the declaration
> and definition are not seen by the same run of the compiler.
>
> - Jonathan M Davis
>