Semantics of +=, -=, ...

[01mf02]

The jq manual states:

jq has a few operators of the form a op= b, which are all equivalent to a |= . op b.

However, I believe that this is actually not true in jq. Proof:

$ jq -cn '{x: 1, y: 2} | .x += .y'
{"x":3,"y":2}
$ jq -cn '{x: 1, y: 2} | .x |= . + .y'
jq: error (at <unknown>): Cannot index number with string "y"

What is the intended semantics of +=, -= then? Should the jq manual be updated to reflect this behaviour?
@itchyny, @pkoppstein, do you have any idea about this?

(I discovered this issue while porting @itchyny's Brainfuck interpreter to jaq, which involved changing
.output += [.memory[.pointer]] to .memory[.pointer] as $m | .output += [$m] due to this issue.)

[wader]

Hi, jqlang/jq#2407 might be interesting

[01mf02]

Hi @wader, thanks, that is definitely interesting!
I particularly like the definition of @pkoppstein:

• V | (E = F) is identical to V | (E = (V|F))
• V | (E |= F) is identical to V | (E = (V|E|F))
• V | (E += F) is identical to V | (E = (V|E) + (V|F))

This seems to be a relatively concise description of the current jq behaviour.

[01mf02]

I adopted the semantics of =, +=, -=, ... that are implemented in jq as of 5908676.