Remove unnecessary type conversion inside qrotation (#38)

* Add failing regression test for #8 (comment)

* Remove unnecessary type conversion.

Addresses #8.

* minor: simplify the "test this doesn't crash" logic

Co-authored-by: Seth Axen <seth.axen@gmail.com>

Co-authored-by: Seth Axen <seth.axen@gmail.com>

src/Quaternion.jl

@@ -208,9 +208,8 @@ function qrotation(axis::Vector{T}, theta) where {T <: Real}
         error("Must be a 3-vector")
     end
     u = normalize(axis)
-    thetaT = convert(eltype(u), theta)
-    s = sin(thetaT / 2)
-    Quaternion(cos(thetaT / 2), s * u[1], s * u[2], s * u[3], true)
+    s = sin(theta / 2)
+    Quaternion(cos(theta / 2), s * u[1], s * u[2], s * u[3], true)
 end
 
 # Variant of the above where norm(rotvec) encodes theta

test/test_Quaternion.jl

@@ -58,6 +58,15 @@ let # test rotations
     @test angle(qrotation([0, 1, 0], pi / 4)) ≈ pi / 4
     @test angle(qrotation([0, 0, 1], pi / 2)) ≈ pi / 2
 
+    # Regression test for
+    # https://github.com/JuliaGeometry/Quaternions.jl/issues/8#issuecomment-610640094
+    struct MyReal <: Real
+      val::Real
+    end
+    Base.:(/)(a::MyReal, b::Real) = a.val / b
+    # this used to throw an error
+    qrotation([1, 0, 0], MyReal(1.5))
+
     let # test numerical stability of angle
         ax = randn(3)
         for θ in [1e-9, π - 1e-9]