Question

A recent question here made use of the default keyword in non-generic code that interests me:

StreamReader r = default(StreamReader);

What is the purpose served here? How is this different from:

StreamReader r;

Both statements define r. In ‘SLaks’ answer below, he clarifies that the use of default additionally sets r to null, but that could be done explicitly by just using null. Is this a style issue, or is there some utility served?

I have used default in generic code (and, of course, in switch statement blocks) but do not understand it’s purpose in this usage.

Answer 1

It’s different from StreamReader r; in that it assigns the variable.
It’s (completely) identical to StreamReader r = null;.

For reference types, default(T) compiles to null.
For value types, default(T) compiles to new T().

C#’s default(T) keyword is actually equivalent to VB.Net’s Nothing keyword.