On Thursday, 19 January 2017 at 02:35:08 UTC, Ignacious wrote:
But this is alias this, the whole point of alias this is to
treat the type as as the alias?
No, alias this is for subtyping. Similar to a child class, a
subtype can be used as its parent type, but must be constructed.
class A {}
class B : A {}
A a = new B(); // legal, B will convert to A
B a = new A(); // illegal, A is not B
alias this is the same concept, just outside of class inheritance.
https://en.wikipedia.org/wiki/Subtyping
Yet, logically, 3 is convertible to Y(3rd line above) and Y is
appendable to X.
Wrong. Implicit construction and implicit conversion are
different concepts in theory and in practice in every language I
know. You often want them separately as construction may need
additional state, may just not be logical, and may have a
different runtime cost than substitution.
D does not support implicit construction under any circumstance
except the typesafe variadic syntax in function calls that take a
single class.
(I'd like to add it, but Walter doesn't agree..)
