On Thursday, 30 December 2021 at 01:04:10 UTC, Ali Çehreli wrote:
The second item in the documentation mentions "any number of
default parameters" when describing copy constructor syntax:
https://dlang.org/spec/struct.html#struct-copy-constructor
1) I can't figure out how to use those extra parameters. For
example, I can't find a special function name to call
explicitly:
S.__cctor(a, 42); // No go
2) Unlike the examples there, I think the parameter should most
usefully be defined as 'const' unless there is a special reason:
struct S {
// const(S) instead of S:
this(ref const(S) that) {
}
}
Do you agree?
Thank you,
Ali
11
A copy constructor always takes one parameter, reference to the
type for which it belongs, there maybe other parameters but they
must have default values.
An copy constructor is called as an copying function and the
purpose of the copy constructor is to create an object of a type
by using an object of the same type as basis for creation of the
new type.
The Standard specify's that the copy constructor be of the type:
T(const &T obj);
This basically allows creation of temporary objects during
calling functions by value or returning objects of the type by
value.
This syntax facilitates creation of an new object as:
T obj1(obj2); <--------- Direct Initialization
T obj1 = obj2; <--------- Copy Initialization
If the additional arguments being passed to the copy constructor
would not be mandated to have default values then the
construction of objects using the above syntax would not be
possible.
Hence the strict condition,
there maybe other parameters to a copy constructor but they must
have default values.
https://acatpg.mn.co/posts/19530612
