JuliaLang/julia

Single argument `isa` function

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#32,018 opened on May 13, 2019

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featurehelp wanted

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Description

It would be nice to have a single argument isa for cleaner filtering code.

filter(x -> !isa(x, AbstractFloat), [1, 2.0])
# could become
filter(!isa(AbstractFloat), [1, 2.0])

This would provide some consistency with other functions, such as isequal, but since isa is a builtin function, defining other variants doesn't seem trivial.

julia> Core.isa(::Type{T}) where {T} = (x) -> isa(x, T)
ERROR: cannot add methods to a builtin function

Contributor guide

Research direction
Examine the implementation of the built in `isa` function in Julia's bootstrapping phase. Explore if it is possible to define a method for builtins via `Core.IntrinsicFunction` or if a wrapper function in Base is required. Check for previous discussions on partial application of builtins.
Tech stack
julia
Domain
compilers
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Julia
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20