Go refusing to make structs in maps mutable since 2012
I've recently asked if it's time to revisit the decision to make structs in maps in Go mutable, and was politely declined, with a reference to this being a refusted proposal since 2012:
https://github.com/golang/go/issues/53857
Since arrays work fine, if a is a slice or an array:
a[10].field = 42
it seems bogus that maps don't; this doesn't compile in Go if m is a map:
m[10].field = 42
In both cases, the address of the struct is calculated at runtime, as it must be known to access the field.
Instead of leaving this as a rant, let's make it a question: what's your "what is this insanity?" peeve with your favourite language?
Comments
It does not seem bogus to me. Values in a map are not addressable for a good reasons. It allows more freedom in implementing a map. Arrays, on the other hand, are specified to be continuous in memory, hence the implementation is set in stone.
Also, non-existent items of a map return the zero value as specified. Now assume the map items are addressable. What exactly should happen if you refer to a field of a map item that is not in the map? Is there a possibility that is not surprising?