On Monday, 12 February 2018 at 08:35:05 UTC, Nathan S. wrote:
For example in std.container.rbtree:
---
auto equalRange(this This)(Elem e)
{
auto beg = _firstGreaterEqual(e);
alias RangeType = RBRange!(typeof(beg));
if (beg is _end || _less(e, beg.value))
// no values are equal
return RangeType(beg, beg);
static if (allowDuplicates)
{
return RangeType(beg, _firstGreater(e));
}
else
{
// no sense in doing a full search, no duplicates
are allowed,
// so we just get the next node.
return RangeType(beg, beg.next);
}
}
---
It's a template this parameter:
https://dlang.org/spec/template.html#template_this_parameter
Simply put, it gets the type of the 'this' parameter when the
function is invoked, with all type modifiers. For a class A with
a subclass B, 'This' would be B if called from B, and const(A)
when called from const(A).
The type of the 'this' parameter is the statically known type,
not the dynamic type. This creates some limitations, as shown
below.
Some examples:
struct S {
void foo(this This)() {
writeln(This.stringof);
}
}
class A {
void foo(this This)() {
writeln(This.stringof);
}
void bar() {
foo();
}
}
class B : A{}
unittest {
S s;
const shared S css;
immutable S iss;
s.foo(); // S
css.foo(); // shared(const(S))
iss.foo(); // immutable(S)
B b = new B();
A a = b;
b.foo(); // B
a.foo(); // A, since typeof(a) == A.
b.bar(); // A, since bar() calls foo() in a context where the
type of 'this' is A.
}
--
Simen
