Scala Buffer: Size or Length?

Question

I am using a mutable Buffer and need to find out how many elements it has.

Both size and length methods are defined, inherited

Answer 1

They are synonyms, as the scaladoc for Buffer.size states:

The size of this buffer, equivalent to length.

The scaladoc for Buffer.length is explicit too:

The length of the buffer. Note: xs.length and xs.size yield the same result.

Simple advice: refer to the scaladoc before asking a question.

UPDATE: Just saw your edit adding mention of performance. As Daniel C. Sobral aid, one is normally always implemented in term of the other, so they have the same performance.