Rename "tuple" to "vector" in SSZ spec

[JustinDrake]

To be done in combination with #777.

Also:

• Define "fixed-size" and "variable-size" more rigorously
• Use " vs ' consistently
• Add missing "

[vbuterin]

👍

[pipermerriam]

I know this was already merged, but what is the motivation on using vector instead of tuple? The tuple language lines up nicely with the concept that already exists in the ABI encoding spec and python's concept of Tuple types.

[pipermerriam]

Was struct considered? Seems like "Struct" would likely carry the most semantic meaning across many languages.

[JustinDrake]

See #777. Basically we want to convey an "ordered fixed-length homogeneous collection of values" in one word. "tuple", "array", "vector", etc. were considered. Python tuples are not homogeneous, and using Tuple may cause a clash with type hinting since we want to be explicit about the length.

struct would be fine for containers. (That's the terminology used in Go.)

[pipermerriam]

👍 I think struct is significantly better than vector, I'll create a PR today unless someone is opposed.

[JustinDrake]

Wait, struct is good for ordered heterogenous collection of values, right? Vector is for homogeneous stuff.

It's unfortunate there's a bikeshedding surface here. At the end of the day, the spec mostly needs to be consistent and implementers will use whatever terminology is most appropriate for their language. (E.g. in Go it would be struct, array, slice instead of container, vector, list.)

[pipermerriam]

blarg, ignore me, shouldn't comment on pull requests first thing in the morning before shower and coffee.

Long live vectors!