A CastConstructor in CeePlusPlus is similar to a CopyConstructor, except that the type of the argument is ''different'' than the type being defined; i.e.

 class Foo {
    public:
      Foo (const Bar &);

      // more stuff
 };

Like the CopyConstructor, the CastConstructor can be invoked either with "standard" constructor syntax:

 Bar b;
 Foo f(b);

or with "assignment" syntax

 Bar b;
 Foo f = b;

But wait...there's more.  The CastConstructor also allows ''implicit'' casts to be performed, like this.

 void snarf_the_foo (Foo &foo);

 ...

 Bar b;
 snarf_the_foo (b); // equivalent to snarf_the_foo (Foo(b));

which can surprise you.  The explicit keyword can be used to disable this automatic conversion.  If Foo is defined as follows:

 class Foo {
    public:
      explicit Foo (const Bar &);

      // more stuff
 };

then silent conversions like that won't occur, and calling snarf_the_foo with a Bar argument will result in a compiler error.  You can still use an explicit cast--i.e. snarf_the_foo (Foo(b)) if you want to do that.


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CategoryCpp