Allow only keyword arguments for DifferentialEvolution`

src/proposals.jl

@@ -64,8 +64,8 @@ end
 
 """
 ```
-DifferentialEvolution(γ0, σ_gamma = 1e-5)
 DifferentialEvolution(; n_para, σ_gamma = 1e-5)
+DifferentialEvolution(; γ0, σ_gamma = 1e-5)
 ```
 
 Differential Evolution proposal, default values corresponding to EMCEE.
@@ -85,13 +85,17 @@ Integrations And Differential Evolution Markov Chain Monte Carlo. ApJS
 struct DifferentialEvolution <: Proposal
     γ0::Float64
     σ_gamma::Float64
-end
-
-DifferentialEvolution(λ0) = DifferentialEvolution(λ0, 1e-5)
 
-function DifferentialEvolution(; n_para, σ_gamma = 1e-5)
-    γ0 = 2.38/sqrt(2*n_para)
-    DifferentialEvolution(γ0, σ_gamma)
+    function DifferentialEvolution(; γ0 = nothing, n_para = nothing, σ_gamma = 1e-5)
+        if !isnothing(γ0) && isnothing(n_para)
+            new(γ0, σ_gamma)
+        elseif !isnothing(n_para) && isnothing(γ0)
+            γ0 = 2.38/sqrt(2*n_para)
+            new(γ0, σ_gamma)
+        else
+            throw(ArgumentError("Provide either `γ0` or `n_para`, not both."))
+        end
+    end
 end
 
 function (de::DifferentialEvolution)(θ, population)

test/runtests.jl

@@ -199,6 +199,15 @@ end
 
 @testset "proposals generation" verbose = true begin
 
+    @testset "constructors" begin
+        # disallow positional arguments
+        @test_throws MethodError DifferentialEvolution(1, 0.1)
+        @test_throws MethodError DifferentialEvolution(1)
+        # you can only pass `γ0` or `n_para`, not both
+        @test_throws ArgumentError DifferentialEvolution(γ0=1, n_para=5)
+        @test_throws ArgumentError DifferentialEvolution(γ0=1, n_para=5, σ_gamma=1.4)
+    end
+
     @testset "1-dim" begin
         ## Define model
         f_dist(θ) = abs(0.0 - mean(rand(Normal(θ[1], 1), 100)))