Make numtype public

NEWS.md

@@ -1,5 +1,9 @@
 # Unitful.jl changelog
 
+## Unreleased
+
+* ![Feature:](https://img.shields.io/badge/-feature-green) `Unitful.numtype` is now part of the public API. It returns the underlying numeric type of a quantity (e.g. `Float64` for `1.0u"m"`), of any `Number` (where it just returns its type), or of a `Base.Enum` (the backing integer type). On Julia ≥ 1.11 the name is declared `public`.
+
 ## v1.28.0 (2026-01-29)
 
 * ![Feature:](https://img.shields.io/badge/-feature-green) Dimensionless quantities now support `iseven` and `isodd` ([#829](https://github.com/JuliaPhysics/Unitful.jl/pull/829)).

docs/src/manipulations.md

@@ -34,6 +34,12 @@ Unitful.dimension
 Unitful.ustrip
 ```
 
+## Numeric type extraction
+
+```@docs
+Unitful.numtype
+```
+
 ## Unit multiplication
 
 ```@docs

src/Unitful.jl

@@ -36,6 +36,11 @@ export @logscale, @logunit, @dB, @B, @cNp, @Np
 export Level, Gain
 export uparse
 
+# Public, but not exported to avoid name clashes (`public` requires Julia ≥ 1.11).
+if VERSION >= v"1.11.0-DEV.469"
+    eval(Meta.parse("public numtype"))
+end
+
 const unitmodules = Vector{Module}()
 
 function _basefactors(m::Module)

src/utils.jl

@@ -1,8 +1,41 @@
 @inline isunitless(::Units) = false
 @inline isunitless(::Units{()}) = true
 
+"""
+    numtype(x::Number)
+    numtype(::Type{T}) where {T<:Number}
+    numtype(x::Base.Enum)
+    numtype(::Type{T}) where {T<:Base.Enum}
+
+Return the underlying numeric type of a number or number type.
+
+For an [`AbstractQuantity`](@ref Unitful.AbstractQuantity), this is the type
+parameter describing the value stored alongside the units. For an `Enum`, it is
+the integer type that backs the enumeration. For a plain `Number`, there is
+nothing to strip, so `numtype` returns its type. Other number-like types can
+extend `numtype` by adding methods.
+
+```jldoctest
+julia> using Unitful
+
+julia> Unitful.numtype(1.0u"m")
+Float64
+
+julia> Unitful.numtype(typeof(1.0u"m"))
+Float64
+
+julia> Unitful.numtype(1 + 2im)
+Complex{Int64}
+```
+"""
+function numtype end
+
+@inline numtype(x::Number) = typeof(x)
+@inline numtype(::Type{T}) where {T<:Number} = T
 @inline numtype(::AbstractQuantity{T}) where {T} = T
 @inline numtype(::Type{Q}) where {T, Q<:AbstractQuantity{T}} = T
+@inline numtype(x::Base.Enum) = numtype(typeof(x))
+@inline numtype(::Type{E}) where {T, E<:Base.Enum{T}} = T
 
 @inline dimtype(u::Unit{U,D}) where {U,D} = D
 

test/runtests.jl

@@ -562,12 +562,34 @@ Unitful.uconvert(U::Unitful.Units, q::QQQ) = uconvert(U, Quantity(q.val, cm))
         # promoting the second time should not change the types
         @test_throws ErrorException promote(px, py)
     end
-    @testset "> Some internal behaviors" begin
+    @testset "> numtype" begin
         # quantities
         @test Unitful.numtype(Quantity{Float64}) <: Float64
         @test Unitful.numtype(Quantity{Float64, 𝐋}) <: Float64
         @test Unitful.numtype(typeof(1.0kg)) <: Float64
         @test Unitful.numtype(1.0kg) <: Float64
+        # plain numbers (public API fallback)
+        @test Unitful.numtype(1) === Int
+        @test Unitful.numtype(1.0) === Float64
+        @test Unitful.numtype(1 + 2im) === Complex{Int}
+        @test Unitful.numtype(1 // 2) === Rational{Int}
+        @test Unitful.numtype(Float64) === Float64
+        @test Unitful.numtype(Complex{Float32}) === Complex{Float32}
+        # Bool is a Number, so it hits the generic fallback
+        @test Unitful.numtype(true) === Bool
+        @test Unitful.numtype(Bool) === Bool
+        # Enums carry their backing integer type as a parameter
+        @eval @enum NumtypeEnum::Int32 numtype_a numtype_b
+        @test Unitful.numtype(numtype_a) === Int32
+        @test Unitful.numtype(NumtypeEnum) === Int32
+        # Do not accidentally support `Union{}`
+        @test_throws MethodError Unitful.numtype(Union{})
+        # not a Number → MethodError
+        @test_throws MethodError Unitful.numtype("not a number")
+        @test_throws MethodError Unitful.numtype(String)
+        if VERSION >= v"1.11.0-DEV.469"
+            @test Base.ispublic(Unitful, :numtype)
+        end
     end
 end