get_precision with multiple arguments

Author: emmt

NEWS.md

@@ -4,6 +4,14 @@ This page describes the most important changes in `TypeUtils`. The format is bas
 [Keep a Changelog](https://keepachangelog.com/en/1.1.0/), and this project adheres to
 [Semantic Versioning](https://semver.org).
 
+## Unreleased
+
+### Added
+
+- With multiple arguments, `get_precision(x, y...)` yields the best precision of all the
+  given arguments.
+
+
 ## Version 1.9.0 (2025-06-20)
 
 This new minor version adds methods to deal with the numerical precision of numbers and

src/precision.jl

@@ -43,6 +43,23 @@ get_precision(::Type{<:Factorization{T}}) where {T} = get_precision(T)
     return r
 end
 
+"""
+    get_precision(x, y, z...) -> T<:AbstractFloat
+
+yields the best precision of all given arguments `x`, `y`, and `z...`.
+
+"""
+@inline get_precision(x, y, z...) = get_precision(get_precision(x, y), z...)
+get_precision(x, y) =
+    get_precision(get_precision(x)::Type{<:AbstractFloat},
+                  get_precision(y)::Type{<:AbstractFloat})::Type{<:AbstractFloat}
+
+get_precision(::Type{AbstractFloat}, ::Type{AbstractFloat}) = AbstractFloat
+get_precision(::Type{T}, ::Type{AbstractFloat}) where {T<:AbstractFloat} = T
+get_precision(::Type{AbstractFloat}, ::Type{T}) where {T<:AbstractFloat} = T
+get_precision(::Type{S}, ::Type{T}) where {S<:AbstractFloat,T<:AbstractFloat} =
+    promote_type(S, T)::Type{<:AbstractFloat}
+
 """
     adapt_precision(T::Type{<:AbstractFloat}, x) -> y
 

test/runtests.jl

@@ -921,6 +921,22 @@ same_value_and_type(x::T, y::T) where {T} = (x === y) || (x == y)
         @test @inferred(get_precision(B)) == Float32
         @test @inferred(get_precision(typeof(B))) == Float32
 
+        # Multiple arguments.
+        @test @inferred(get_precision(Int8, Int)) == AbstractFloat
+        @test @inferred(get_precision(Int8, Int, BigFloat)) == BigFloat
+        @test @inferred(get_precision(String, Float16)) == Float16
+        @test @inferred(get_precision(:hello, Float16)) == Float16
+        @test @inferred(get_precision(:hello, zero(Float16))) == Float16
+        @test @inferred(get_precision(Symbol, zero(Float16))) == Float16
+        @test @inferred(get_precision(Float16, String)) == Float16
+        @test @inferred(get_precision(Float16, :hello)) == Float16
+        @test @inferred(get_precision(zero(Float16), :hello)) == Float16
+        @test @inferred(get_precision(zero(Float16), Symbol)) == Float16
+        @test @inferred(get_precision(Float32, Int)) == Float32
+        @test @inferred(get_precision(Float32, Int, pi)) == Float32
+        @test @inferred(get_precision(Float32, Int, pi, 1.0)) == Float64
+        @test @inferred(get_precision(Float32, Int, pi, 1.0)) == Float64
+        @test @inferred(get_precision(Float32, Int, pi, big(1.0))) == BigFloat
     end
 
     @testset "adapt_precision" begin