Improve name scope in typescript for multi-initialization statements

[pokey]

The problem

In code like the following:

const aaa = 0, bbb = 1;

we could improve our support for the name scope.

The solution

We should probably handle the case of a simple initializer with only one variable separately from a multi-child one

Single-variable initializer

For example:

const aaa = 0;

In this case, we want the following:

• A single scope whose domain is the entire statement

This way you could say:

• "name" from within the statement to get the name
• "every name" from anywhere in the block containing the statement (including within statement itself) to get all the names in that block

Multi-variable initializer

For example:

const aaa = 0, bbb = 1;

In this case, we want the following:

• one scope per nested assignment (aaa = 0 and bbb = 1)
• a parent scope whose domain is the entire statement, and has multiple content ranges, one per sub-assignment name
• an iteration scope that is the entire statement

This way you could say:

• "name" from within a sub-assignment to get the name of that sub-assignment
• "name" from the start / end of the statement to get all the names in that statement
• "every name" from anywhere in the statement to get all the names in that statement
• "first name" from anywhere in the statement to get the first name in that statement
• "every name" from anywhere in the block containing the statement, except within statement itself, to get all the names in that block

Discussion

Note that we may want to use this pattern in other places

• Talon condition blocks
• Go return values
• Tags in .scm files

[auscompgeek]

Would you also want the same sort of thing in Python tuple unpacking?

[pokey]

Good question. My instinct is to say no. For that it's generally more useful to just target the entire left-hand side. But I think @josharian wants something like that for Go, so maybe we should discuss

[josharian]

Yeah, in Go, code like this is very common:

x, err := foo()

and wanting to refer to just x or err individually is also going to be very common.

(It's not tuple unpacking, it's multiple assignment, but it's very similar.)

[pokey]

I guess you'd want to be able to say eg "chuck first name", "pour last name", etc?

[josharian]

Yeah, after a refactor that changes what a function returns, it's going to be very common to want to chuck or pour or clone or swap individual names.