1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
|
So do we have to define yet another overloaded function template, this
time expecting tt(Type *) arguments? It is possible, but at some point it
should become clear that our approach doesn't scale. Like ordinary functions
and classes, function templates should have one conceptually clear
purpose. Trying to add overloaded function templates to overloaded function
templates quickly turns the template into a kludge. Don't use this approach. A
better approach is to construct the template so that it fits its original
purpose, to make allowances for the occasional specific case and to describe
its purpose clearly in its documentation.
In some situations constructing template explicit specializations may of
course be defensible. Two specializations for tt(const) and non-tt(const)
pointers to characters might be appropriate for our tt(add) function
template. hi(template: explicit specialization) Here's how they are
constructed:
itemization(
it() Start with the keyword tt(template).
it() Next, an empty set of angle brackets is written. This indicates to
the compiler that there must be an em(existing) template whose prototype
matches the one we're about to define. If we err and there is no such template
hi(template: id-declaration mismatch)
then the compiler reports an error like:
verb( error: template-id `add<char*>' for `char* add(char* const&, char*
const&)' does not match any template declaration)
it() Now the function's head is defined. It must match the prototype of
the initial function template or the form of a template explicit instantiation
declaration (see section ref(TEMPFUNEXDEC)) if its specialized type cannot be
determined from the function's arguments. It must specify the correct
returntype, function name, maybe explicit template type arguments, as well as
the function's parameter list.
it() Finally the function's body is defined, providing the special
implementation that is required for the specialization.
)
Here are two explicit specializations for the function template tt(add),
expecting tt(char *) and tt(char const *) arguments:
verb( template <> char *add<char *>(char *const &p1,
char *const &p2)
{
std::string str(p1);
str += p2;
return strcpy(new char[str.length() + 1], str.c_str());
}
template <> char const *add<char const *>(char const *const &p1,
char const *const &p2)
{
static std::string str;
str = p1;
str += p2;
return str.c_str();
})
Template explicit specializations are normally included in the file
containing the other function template's implementations.
|
