On Sunday, 13 September 2015 at 09:29:13 UTC, Enamex wrote:
On Sunday, 13 September 2015 at 08:26:55 UTC, Alexandru
Ermicioi wrote:
Hello,
Given:
class SomeClass {
public {
void someSimpleMethod() {}
template setOfTemplatedMethods(Type) {
void templatedMethodOne() {}
void templatedMethodTwo() {}
}
}
}
Is there a way to detect at compile time if a member of
class/struct is a template? (in the example above, if
setOfTemplatedMethods is a template).
There's this:
http://stackoverflow.com/questions/5483381/test-if-an-alias-is-a-template-in-d-2-0
and it should work with 'member templates' OK.
Thx for the provided link.
I've tried to implement version from the stackoverflow answer,
and run against tests provided in another answer to the question
in link, and failed.
With dmd version 2.067.1 this implementation fails at
static assert(! isTemplate!(FooS!int.func!float) );
static assert(! isTemplate!(FooS!int.bar) );
for .func it requires "this" (an value of type FooS, or
isTemplate fails to instantiate).
and for .bar it just fails (isTemplate detects it as a template).
I've found another way to detect if a symbol is a template.
The idea is that for a not instantiated template you can get with
allMembers trait the list of members in template, but you can't
access them using getMembers trait since the template is not
instantiated yet.
So if there is a symbol that has members which cannot be accessed
using getMember (generates an error) then this is a template!
template allMembers(alias Type) {
alias allMembers = TypeTuple!(__traits(allMembers, Type));
}
template anyAccessible(alias Container, T...) {
static if (T.length > 1) {
enum bool anyAccessible = anyAccessible!(Container, T[0
.. $ / 2]) || anyAccessible!(Container, T[$ / 2 .. $]);
} else static if (T.length == 1) {
enum bool anyAccessible = __traits(compiles,
getMember!(Container, T[0]));
} else {
enum bool anyAccessible = false;
}
}
template isTemplate(alias T) {
static if ( // check if symbol has members
__traits(compiles, TypeTuple!(__traits(allMembers, T)))
&& !T.stringof.startsWith("module ", "package ")
) {
enum bool isTemplate =
(allMembers!(T).length > 0)
&& !anyAccessible!(T, allMembers!T);
} else {
enum bool isTemplate = false;
}
}
It passes almost all tests except for:
static assert(! isTemplate!((int x){return x;}) );
static assert(! isTemplate!(std) );
static assert(! isTemplate!(core) );
I don't know how but in this cases, compiler attempts to parse
true branch of static if, even if the expression in static if is
false.
For lamda function allMembers trait fails to get the members and
an error is created by compiler.
For std, and core packages isTemplate evaluates to true even if
expression from static if is false.
Is such behavior of static if correct (tested also with ldc
compiler, same results)?
If there are other test cases, would be glad if they are posted
here (to improve the accuracy of template detection).
Tests are:
struct FooS(T) {
struct Inner {}
struct Inner2(string U="!(") {}
int func(U)() { return 0; }
int bar;
}
FooS!int foo;
class FooC { int x; }
union FooU { int x;}
enum FooE { x }
interface FooI { int x(); }
template FooT(T) {
struct Inner {}
struct Inner2(string U="!(") {}
int func(U)() { return 0; }
int bar;
}
static assert(! isTemplate!0 );
static assert(! isTemplate!"0" );
static assert(! isTemplate!0.0f );
static assert(! isTemplate!'0' );
static assert(! isTemplate!'!' );
static assert(! isTemplate!"module std.stdio" );
static assert(! isTemplate!null );
static assert(! isTemplate!true );
static assert(! isTemplate!__FILE__ );
static assert(! isTemplate!__LINE__ );
static assert(! isTemplate!([]) );
static assert( isTemplate!FooS );
static assert(! isTemplate!(FooS!int) );
static assert( isTemplate!(FooS!int.func) );
static assert(! isTemplate!(FooS!int.func!float) );
static assert(! isTemplate!(FooS!int.bar) );
static assert(! isTemplate!(FooS!int.Inner) );
static assert( isTemplate!(FooS!int.Inner2) );
static assert(! isTemplate!(FooS!int.Inner2!"?") );
static assert( isTemplate!FooT );
static assert(! isTemplate!(FooT!int) );
static assert( isTemplate!(FooT!int.func) );
static assert(! isTemplate!(FooT!int.func!float) );
static assert(! isTemplate!(FooT!int.bar) );
static assert(! isTemplate!(FooT!int.Inner) );
static assert( isTemplate!(FooT!int.Inner2) );
static assert(! isTemplate!(FooT!int.Inner2!"?") );
static assert(! isTemplate!foo );
static assert( isTemplate!(foo.func) );
static assert( isTemplate!isTemplate );
static assert(! isTemplate!(isTemplate!isTemplate) );
static assert(! isTemplate!FooC );
static assert(! isTemplate!FooU );
static assert(! isTemplate!FooE );
static assert(! isTemplate!FooI );
static assert(! isTemplate!((int x){return x;}) );
static assert( isTemplate!(std.stdio.writefln) );
static assert(! isTemplate!(std.stdio) );
static assert(! isTemplate!std );
static assert(! isTemplate!(core) );
