Modern SharedPtr SpCast

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SpCast

Returns a SharedPtr to a base type that shares ownership with the derived one.

Syntax

SpCast( of D, B )

Examples

#import "std/memory"
using memory

type Shape extends Object
    as int32 id
    declare virtual destructor( )
end type
virtual destructor Shape( ) : end destructor

type Circle extends Shape
end type

dim d as SharedPtr( of Circle ) = MakeShared( of Circle )( )
d.Ref( ).id = 7

'' Both type arguments must be written out: inference reads parameter
'' positions only, and the target type appears in none of them
dim b as SharedPtr( of Shape ) = SpCast( of Circle, Shape )( d )

print b.Ref( ).id            '' 7
print b.UseCount( )          '' 2 -- one object, two handles, shared count

'' THE BASE MUST HAVE A VIRTUAL DESTRUCTOR: the returned handle destroys
'' through `delete cptr( Shape ptr, obj )`, and nothing here can check it.
'' (The type is not called Base because BASE is a tiko keyword.)

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Library: SharedPtr and WeakPtr
Category: Smart Pointers
Documented under: Members