Declarations vs definitions

Question

In C# how does a declaration differ from a definition, i.e.:

1. A class declaration vs a class definition
2. A variable declaration vs definition
3. A met

Answer 1

The C++ build model dates from an era where ferrite cores were a dollar a dozen. Multiple source code files compiled one at a time. With a single-pass compiler. A linker to glue everything together. That made separate declarations in header files and prototypes necessary.

The C# compiler takes ready advantage of modern machine resources. All source code files that constitute an assembly are compiled at the same time, the compiler makes at least two passes so it can parse declarations before method bodies. There's still a possible link model but it gets very rarely used.

The only notions of a declaration having to match a definition that I can think of is a delegate type having to match a target method and an interface member declaration having to match its concrete implementation.