From d769f4de322ce0b40bf04681c826ea7d73681325 Mon Sep 17 00:00:00 2001
From: ouchinao <ouchi.nao.jg@tut.jp>
Date: Wed, 8 Jul 2026 02:10:20 +0900
Subject: [PATCH] Raise a helpful ArgumentError for non-hash context

Passing a non-hash argument to `.call` previously failed with a cryptic
"undefined method `each_pair'" error. Context.build now raises an
ArgumentError explaining that keyword arguments were likely intended.

nil and any object responding to #each_pair are still accepted.

Closes #178

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 lib/interactor/context.rb       |  9 ++++++++-
 spec/interactor/context_spec.rb | 25 +++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/lib/interactor/context.rb b/lib/interactor/context.rb
index 1402e60..742c6c5 100644
--- a/lib/interactor/context.rb
+++ b/lib/interactor/context.rb
@@ -52,11 +52,18 @@ class Context < OpenStruct
     #   # => 2170969340
     #
     # Returns the Interactor::Context.
+    # Raises ArgumentError if the argument is not nil, an Interactor::Context
+    #   or an object responding to each_pair (like a Hash).
     def self.build(context = {})
       if self === context
         context
-      else
+      elsif context.nil? || context.respond_to?(:each_pair)
         new(context)
+      else
+        raise ArgumentError,
+          "Expected a Hash or an object responding to #each_pair, " \
+          "got #{context.class}. Did you mean to pass keyword arguments? " \
+          "(e.g. MyInteractor.call(foo: \"bar\"))"
       end
     end
 
diff --git a/spec/interactor/context_spec.rb b/spec/interactor/context_spec.rb
index d990479..c3fd708 100644
--- a/spec/interactor/context_spec.rb
+++ b/spec/interactor/context_spec.rb
@@ -27,6 +27,31 @@ module Interactor
         }
       end
 
+      it "builds an empty context if nil is given" do
+        context = Context.build(nil)
+
+        expect(context).to be_a(Context)
+        expect(context.send(:table)).to eq({})
+      end
+
+      it "accepts any object responding to #each_pair" do
+        hash_like = double(:hash_like)
+        allow(hash_like).to receive(:each_pair) do |&block|
+          {foo: "bar"}.each_pair(&block)
+        end
+
+        context = Context.build(hash_like)
+
+        expect(context).to be_a(Context)
+        expect(context.foo).to eq("bar")
+      end
+
+      it "raises a helpful error when given a non-hash argument" do
+        expect {
+          Context.build("baz")
+        }.to raise_error(ArgumentError, /String/)
+      end
+
       it "preserves an already built context" do
         context1 = Context.build(foo: "bar")
         context2 = Context.build(context1)