Fix Currency.unregister before the currency table is loaded

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Fix `Money::Currency.unregister` raising `NoMethodError` when called before the currency table was loaded, for example in an initializer right after `require "money"`
 - Fix `Money::Allocation.generate` converting a Rational with unlimited `to_d` precision. It now uses `Money.conversion_precision`
 - Fix `Money::Currency.reset!` keeping the cached key set, so a currency registered before the reset was still accepted by `Money::Currency.new` and raised `NoMethodError` instead of `UnknownCurrency`
 - Fix `Money::Bank::VariableExchange#import_rates` parsing `:json` with `JSON.load`, which instantiates any class named by a `json_class` key; it now uses `JSON.parse`

lib/money/currency.rb

@@ -204,8 +204,12 @@ def unregister(curr)
           else
             curr.downcase.to_sym
           end
-        existed = @table.delete(key)
-        @stringified_keys = nil if existed
+        existed = table.delete(key)
+        if existed
+          @@mutex.synchronize { _instances.delete(key.to_s) }
+          @stringified_keys = nil
+          clear_iso_numeric_cache
+        end
         existed ? true : false
       end
       # rubocop:enable Naming/PredicateMethod

spec/money/currency_spec.rb

@@ -241,6 +241,32 @@ def to_s
       described_class.unregister(:yyz)
       expect(described_class.find(:yyz)).to be_nil
     end
+
+    context "when the currency table changes" do
+      after { described_class.reset! }
+
+      it "works before the currency table has been loaded" do
+        described_class.instance_variable_set(:@table, nil)
+
+        expect(described_class.unregister(:usd)).to be true
+        expect(described_class.find(:usd)).to be_nil
+        expect(described_class.find(:eur)).to eq described_class.new(:eur)
+      end
+
+      it "returns false for an unknown currency before the table has been loaded" do
+        described_class.instance_variable_set(:@table, nil)
+
+        expect(described_class.unregister(:abc)).to be false
+      end
+
+      it "drops the currency from the iso_numeric lookup" do
+        expect(described_class.find_by_iso_numeric(978)).to eq described_class.new(:eur)
+
+        described_class.unregister(:eur)
+
+        expect(described_class.find_by_iso_numeric(978)).to be_nil
+      end
+    end
   end
 
   # rubocop:disable Style/MapIntoArray