andyferris / freeze.jl

Experimental API for mutable/immutable collections

Freeze.jl

A minimal package to expose an interface for reasoning about and controlling the mutability of indexable containers, via:

• issettable(x) returns a Bool indicating whether setindex! works on x.
• freeze(x) returns a container with the values contained within x that cannot be mutated via setindex!.
• thaw(x) is the reverse of freeze, returning a container with the values contained with x that can be mutated via setindex!.

In the general case, the above might require copying the contents of x, but in practice we expect the Julia compiler to become good at reasoning about the lifetime of objects via escape analysis (as it can already do for structs).

NOTE: The current implementation here for AbstractArray might be unsound because it does not perform defensive copying! This package provides interface guarantees around setindex! only - actual values may mutate if the underlying data structures are accessed directly. It may be useful for experimentation or preventing some varieties of bugs.

See also Base.Experimental.Const in Julia 1.3 onwards, and the ArrayInterface.jl package.

freeze.jl's Issues

Shape-frozen and value-frozen collections

Continuing discussion JuliaArrays/StaticArrays.jl#745 (comment)

If you are going to think about these things remember that append-only datasets are a thing and that we might want eg a vector that supports push! but not setindex!.

Yes, exactly my thought. It'd be great if we can freeze/thaw push!-ability and setindex!-ability separately.

For dictionaries I was thinking isinsertable, freezekeys and thawkeys could be the (orthogonal) “shape” interface.

FYI, I'm using internal "trait" functions like implements(f!, T) and possible(f!, args...) in BangBang.jl as I don't want to keep introducing new trait functions. A similar approach could be useful if you want to distinguish append-only, FIFO, LIFO, etc. But maybe this kind of generality is not appropriate at this stage of design.

As for the naming, I think it'd be nice if "shape freezing/thawing" for vectors and dictionaries can be done with a same interface. I was thinking something like ismutablevalue and ismutableindex but I think "keys" instead of "index" is also fine since keys is implemented for arrays.