add setindex for named tuples

base/namedtuple.jl

@@ -300,3 +300,27 @@ function structdiff(a::NamedTuple{an}, b::Union{NamedTuple{bn}, Type{NamedTuple{
         NamedTuple{names,types}(map(n->getfield(a, n), names))
     end
 end
+
+"""
+    setindex(nt::NamedTuple, val, key::Symbol)
+
+Constructs a new `NamedTuple` with the key `key` set to `val`.
+If `key` is already in the keys of `nt`, `val` replaces the old value.
+
+```jldoctest
+julia> nt = (a = 3,)
+(a = 3,)
+
+julia> Base.setindex(nt, 33, :b)
+(a = 3, b = 33)
+
+julia> Base.setindex(nt, 4, :a)
+(a = 4,)
+
+julia> Base.setindex(nt, "a", :a)
+(a = "a",)
+```
+"""
+function setindex(nt::NamedTuple, v, idx::Symbol)
+    merge(nt, (; idx => v))
+end

test/namedtuple.jl

@@ -267,3 +267,11 @@ let n = NamedTuple{(:T,), Tuple{Type{Float64}}}((Float64,))
     @test n isa NamedTuple{(:T,), Tuple{Type{Float64}}}
     @test n.T === Float64
 end
+
+# setindex
+let nt0 = NamedTuple(), nt1 = (a=33,), nt2 = (a=0, b=:v)
+    @test Base.setindex(nt0, 33, :a) == nt1
+    @test Base.setindex(Base.setindex(nt1, 0, :a), :v, :b) == nt2
+    @test Base.setindex(nt1, "value", :a) == (a="value",)
+    @test Base.setindex(nt1, "value", :a) isa NamedTuple{(:a,),<:Tuple{AbstractString}}
+end