# Meaning of "maybe" in function names and types

**URL:** <https://discourse.julialang.org/t/meaning-of-maybe-in-function-names-and-types/139317>\
**Category:** New to Julia\
**Tags:** modelingtoolkit\
**Created:** [September 9, 2026, 5:30pm UTC](https://discourse.julialang.org/t/meaning-of-maybe-in-function-names-and-types/139317 "2026-09-09T17:30:41Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![mark.garnett](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@mark.garnett](https://discourse.julialang.org/u/mark.garnett)\
**Post date:** [September 9, 2026, 5:30pm UTC](https://discourse.julialang.org/t/meaning-of-maybe-in-function-names-and-types/139317/1 "2026-09-09T17:30:41Z")

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Hi all,

I often see the word “maybe” in function names especially in ModelingToolkit.  
for example “maybe\_build\_initialization\_problem()” or “MaybeArrayIndexT”

Is this a common convention in Julia? What does it mean?

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**Author:** ![kellertuer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kellertuer/32/220707_2.png) [@kellertuer](https://discourse.julialang.org/u/kellertuer)\
**Post date:** [September 10, 2026, 5:29am UTC](https://discourse.julialang.org/t/meaning-of-maybe-in-function-names-and-types/139317/2 "2026-09-10T05:29:31Z")

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I am not aware there is a common understanding or fixed use.

Until now I have seen it in the sense of ensuring something. For your function `maybe_build_X()` is probably means “build X if it was not build yet – or check whether it needs to be build at all”. Maybe more precise would be something with “enusre” (that it is build if needed)

For types I indeed have not yet seen it yet. I personally prefer to have types precise.

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**Author:** ![Sevi](https://avatars.discourse-cdn.com/v4/letter/s/c67d28/32.png) [@Sevi](https://discourse.julialang.org/u/Sevi)\
**Post date:** [September 10, 2026, 1:49pm UTC](https://discourse.julialang.org/t/meaning-of-maybe-in-function-names-and-types/139317/3 "2026-09-10T13:49:19Z")

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I agree, I don’t think that it has a standard meaning across packages or ecosystems.

Where I have seen it used for types is e.g. in Configurations.jl where `Maybe{T}` is just an alias for `Union{T, Nothing}`. I think it makes sense here since the goal is to write “configuration structs” (or parameter structs) where you might have fields that can have a value of type `T`, but there is no meaningful default value, so `nothing` can be used instead (to turn off some functionality altogether for instance).

Another example (kind of) are `DataFrame`s from DataFrames.jl. The element type of a column is sometimes inferred to be `Union{T, Missing}` if not all rows contain an element (when printing, this shows up as `T?` which I find pretty clever), but it might as well be named `Maybe{T}` because when you read elements from that column, you _maybe_ get an actual `T` or … something else (but it’s not called that).

But it’s very context-specific and, as @kellertuer mentioned, types usually benefit from being concrete. But a `Maybe{T}` will probably perform better than `Any`.

This meaning for types (either `T` or some placeholder type) is also found in other languages as far as I recall (Rust?).

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**Author:** ![mikmoore](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mikmoore/32/31109_2.png) [@mikmoore](https://discourse.julialang.org/u/mikmoore)\
**Post date:** [September 10, 2026, 3:37pm UTC](https://discourse.julialang.org/t/meaning-of-maybe-in-function-names-and-types/139317/4 "2026-09-10T15:37:28Z")

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I haven’t discerned a strong convention around the (handful of) `maybeX` functions I’ve seen. But sometimes I’ll write my own to perform certain operations. Especially to add to or modify functionality of existing functions without [piracy](https://docs.julialang.org/en/v1/manual/style-guide/#avoid-type-piracy).

For example, one function I’ve written is this (it could be written better – for example to evaluate the entries of `p` individually – but this was sufficient for my needs):

```julia
using LinearAlgebra # for UniformScaling
maybematrixpoly(x, p) = evalpoly(x, p)
function maybematrixpoly(x::Union{AbstractMatrix, UniformScaling}, p)
    if eltype(p) <: Number # scalar coefficients
        return evalpoly(x, UniformScaling.(p))
    else
        return evalpoly(x, p)
    end
end

```

The intent is to be the same as `evalpoly`, but to work on both numbers and (square) matrices. `evalpoly` on its own did not work because it cannot apply scalar polynomial coefficients to a matrix (because it would attempt to add a number to a matrix). So for the case of matrix polynomials with scalar coefficients, it promotes the coefficients to `UniformScaling` (scaled identity matrices).

Here’s (my recollection of) another function I’ve used before. I had code where I wanted to `copy` a generic object that I didn’t know much about in advance. The issue is that most immutables don’t have a `copy` method so I couldn’t just call `copy` on them. I can’t find the original any more but it looked something like this:

```julia
maybecopy(x) = copy(x)
# add exceptions as necessary
maybecopy(x::String) = x # not copyable and copy not necessary
maybecopy(x::Symbol) = x # not copyable and copy not necessary
maybecopy(x::Nothing) = x # not copyable and copy not necessary
# maybecopy(x::Tuple) = maybecopy.(x) # if you want Tuple fields handled recursively
# maybecopy(x::Tuple) = x # if you want Tuples not copied

```

If I ran into a type that couldn’t `copy`, I would add a method here with the behavior I wanted. I won’t strongly advocate for this one in particular, however, as it might be code smell to need this (hard to find a consolidated place with full discussion, but see some at [#57219](https://github.com/JuliaLang/julia/issues/57219)). Still, it’s much better to do something like this than pirate the original function.

One `maybe`-flavored function (though without the name) in `Base` is [`get`](https://docs.julialang.org/en/v1/base/collections/#Base.get).

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**Author:** ![Benny](https://avatars.discourse-cdn.com/v4/letter/b/49beb7/32.png) [@Benny](https://discourse.julialang.org/u/Benny)\
**Post date:** [September 11, 2026, 12:55am UTC](https://discourse.julialang.org/t/meaning-of-maybe-in-function-names-and-types/139317/5 "2026-09-11T00:55:17Z")

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`Base` has an internal `mightalias` too