MaybeInplace

MaybeInplace.jl solves a common problem in Julia: code written for mutable arrays often fails when used with immutable arrays (like StaticArrays). This package provides macros (@bb, @bangbang, or @❗) that automatically rewrite operations to work with both mutable and immutable arrays, choosing in-place operations when possible and out-of-place operations when necessary.

Installation

MaybeInplace is a   Julia Language   package. To install MaybeInplace, please open Julia's interactive session (known as REPL) and press ] key in the REPL to use the package mode, then type the following command

pkg> add MaybeInplace

Quick Example

using MaybeInplace, StaticArrays

# Without @bb: This function only works with mutable arrays
function add_arrays!(result, a, b)
    result .= a .+ b
    return result
end

# Works with regular arrays
add_arrays!([0.0, 0.0], [1.0, 2.0], [3.0, 4.0])  # ✓ Works

# Fails with StaticArrays (immutable)
# add_arrays!(@SVector[0.0, 0.0], @SVector[1.0, 2.0], @SVector[3.0, 4.0])  # ✗ Error!

# With @bb: This function works with both mutable and immutable arrays
function add_arrays_generic!(result, a, b)
    @bb result .= a .+ b
    return result
end

# Works with regular arrays (uses in-place operation)
add_arrays_generic!([0.0, 0.0], [1.0, 2.0], [3.0, 4.0])  # ✓ Returns [4.0, 6.0]

# Also works with StaticArrays (uses out-of-place operation)
add_arrays_generic!(@SVector[0.0, 0.0], @SVector[1.0, 2.0], @SVector[3.0, 4.0])  # ✓ Returns @SVector[4.0, 6.0]

How It Works

The @bb macro inspects the array at runtime and chooses the appropriate operation. For example:

@bb @. x = y + z

becomes:

if setindex_trait(x) === CanSetindex()
    @. x = y + z  # In-place for mutable arrays
else
    x = @. y + z  # Out-of-place for immutable arrays
end

Supported Operations

The macro supports the following operations:

1. copyto!(y, x) - Copy operations
2. x .= <expr> - Broadcasting assignment
3. @. <expr> - Broadcast macro
4. x .+= <expr>, x .-= <expr>, x .*= <expr>, x ./= <expr> - Compound assignment operators
5. x = copy(y) - Copy with assignment
6. x = similar(y) - Similar array creation
7. x = zero(y) - Zero initialization
8. axpy!(a, x, y) - BLAS-style operations
9. x = y × z - Custom matrix multiplication operator (typed with \times<tab>)

For a complete list and detailed examples, see the docstring: ?@bb