make measurements work with at-printf (#102)

* make measurements work with at-printf

* move 'import Printf' to src/show.jl

Project.toml

@@ -6,6 +6,7 @@ version = "2.5.0"
 [deps]
 Calculus = "49dc2e85-a5d0-5ad3-a950-438e2897f1b9"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
+Printf = "de0858da-6303-5e67-8744-51eddeeeb8d7"
 RecipesBase = "3cdcf5f2-1ef4-517c-9805-6587b60abb01"
 Requires = "ae029012-a4dd-5104-9daa-d747884805df"
 

src/show.jl

@@ -15,6 +15,8 @@
 #
 ### Code:
 
+import Printf
+
 function truncated_print(io::IO, m::Measurement, error_digits::Int;
                          atbeg = "", atend = "", pm = "±")
     val = if iszero(m.err) || !isfinite(m.err)
@@ -88,6 +90,10 @@ function Base.alignment(io::IO, measure::Measurement)
         (length(m.captures[1]), length(m.captures[2]))
 end
 
+if VERSION >= v"1.6.0-rc1"
+    Printf.tofloat(measure::Measurement) = Printf.tofloat(measure.val)
+end
+
 ### Juno pretty printing
 @require Juno="e5e0dc1b-0480-54bc-9374-aad01c23163d" begin
     Juno.render(i::Juno.Inline, measure::Measurement) =

test/runtests.jl

@@ -1,5 +1,5 @@
 using Measurements, SpecialFunctions, QuadGK, Calculus
-using Test, LinearAlgebra, Statistics, Unitful
+using Test, LinearAlgebra, Statistics, Unitful, Printf
 
 import Base: isapprox
 import Measurements: value, uncertainty
@@ -628,6 +628,15 @@ end
         # the same number (note that the tag will be different, but that's not important here).
         for a in (w, x, y); @test eval(Meta.parse(repr(a))) == a; end
     end
+    if VERSION >= v"1.6.0-rc1"
+        @testset "@printf" begin
+            for T in (Float16, Float32, Float64, BigFloat)
+                m1 = measurement(one(T))
+                @test_nowarn @printf("Testing @printf: %.2e\n", m1)
+                @test @sprintf("Testing @sprintf: %.2e\n", m1) == "Testing @sprintf: 1.00e+00\n"
+            end
+        end
+    end
 end
 
 @testset "sum" begin
@@ -851,7 +860,7 @@ end
     @test m .* (1:2:6) isa StepRangeLen
     @test (1:.1:6) .- m isa StepRangeLen
     @test m ./ (1:6.0) isa Vector{<:Measurement}
-    
+
     # JuliaLang/julia#30944
     @test range(0±0, step=1±.1, length=10) isa StepRangeLen
 end