Add fraction_field_type

Author: fingolfin

src/Fraction.jl

@@ -828,6 +828,38 @@ function fraction_field(F::Field; cached::Bool=true)
    return F
 end
 
+
+@doc raw"""
+    fraction_field_type(a)
+
+Return the type of the base ring of the given element, element type, parent or parent type $a$.
+
+# Examples
+```jldoctest
+julia> R, x = polynomial_ring(ZZ, :x)
+(Univariate polynomial ring in x over integers, x)
+
+julia> fraction_field_type(R) == typeof(base_ring(R))
+true
+
+julia> fraction_field_type(zero(R)) == typeof(base_ring(zero(R)))
+true
+
+julia> fraction_field_type(typeof(R)) == typeof(base_ring(R))
+true
+
+julia> fraction_field_type(typeof(zero(R))) == typeof(base_ring(zero(R)))
+true
+```
+"""
+fraction_field_type(x) = fraction_field_type(typeof(x))
+fraction_field_type(x::Type{<:RingElement}) = fraction_field_type(parent_type(x))
+fraction_field_type(T::DataType) = throw(MethodError(fraction_field_type, (T,)))
+
+fraction_field_type(::Type{T}) where {T <: Field} = T
+fraction_field_type(::Type{T}) where {T <: Ring} = AbstractAlgebra.Generic.FracField{elem_type(T)}
+
+
 @doc raw"""
     factored_fraction_field(R::Ring; cached::Bool=true)
 

src/exports.jl

@@ -227,6 +227,7 @@ export find_pivot_popov
 export finish
 export fit!
 export fraction_field
+export fraction_field_type
 export free_associative_algebra
 export free_associative_algebra_type
 export free_module