[Issue 2616] New: Undocumented behaviour: part-explicit, part-implicit instantiations of function templates are accepted

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=2616

           Summary: Undocumented behaviour: part-explicit, part-implicit
                    instantiations of function templates are accepted
           Product: D
           Version: 1.039
          Platform: PC
               URL: http://www.digitalmars.com/d/1.0/template.html
        OS/Version: Windows
            Status: NEW
          Keywords: accepts-invalid, spec
          Severity: normal
          Priority: P2
         Component: www.digitalmars.com
        AssignedTo: bugzilla at digitalmars.com
        ReportedBy: smjg at iname.com
OtherBugsDependingO 2599
             nThis:


`Function templates can be explicitly instantiated with a
!(TemplateArgumentList):

writefln("The square of %s is %s", 3, Square!(int)(3));

or implicitly, where the TemplateArgumentList is deduced from the types of the
function arguments:

writefln("The square of %s is %s", 3, Square(3));  // T is deduced to be int`

It's just come to my attention that the compiler allows an in-between case that
isn't covered by the current documentation, either for D1 or for D2.

----------
import std.stdio;

void fun(T1, T2)(T2 x) {
    pragma(msg, T1.stringof);
    writefln(x);
}

void main() {
    fun!(int)("hello!");
}

----------
C:\Users\Stewart\Documents\Programming\D\Tests>dmd template_partial.d
int

C:\Users\Stewart\Documents\Programming\D\Tests>template_partial
hello!
----------

What is T2?  The template instantiation is explicit in form, but doesn't match
the parameter list with which the template is declared.  Neither is T2 deduced
from the given template arguments.  Neither is it IFTI as currently documented,
since a template parameter list has been given.  Rather, the template
instantiation is of an undocumented mix of the two styles.

Issue 2599 comment 6 implies that this feature is intended, but you forgot to
document it.


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