Add Context#to_a

spec/backtracer/backtrace/frame/context_spec.cr

@@ -1,6 +1,37 @@
 require "../../../spec_helper"
 
+def with_foo_context
+  yield Backtracer::Backtrace::Frame::Context.new(
+    lineno: 10,
+    pre: %w[foo bar baz],
+    line: "violent offender!",
+    post: %w[boo far faz],
+  )
+end
+
 describe Backtracer::Backtrace::Frame::Context do
+  describe ".to_a" do
+    it "works with empty #pre and #post" do
+      context = Backtracer::Backtrace::Frame::Context.new(
+        lineno: 1,
+        pre: %w[],
+        line: "violent offender!",
+        post: %w[],
+      )
+      context.to_a.should eq(["violent offender!"])
+    end
+
+    it "returns array with #pre, #line and #post strings" do
+      with_foo_context do |context|
+        context.to_a.should eq([
+          "foo", "bar", "baz",
+          "violent offender!",
+          "boo", "far", "faz",
+        ])
+      end
+    end
+  end
+
   describe ".to_h" do
     it "works with empty #pre and #post" do
       context = Backtracer::Backtrace::Frame::Context.new(
@@ -13,21 +44,17 @@ describe Backtracer::Backtrace::Frame::Context do
     end
 
     it "returns hash with #pre, #line and #post strings" do
-      context = Backtracer::Backtrace::Frame::Context.new(
-        lineno: 10,
-        pre: %w[foo bar baz],
-        line: "violent offender!",
-        post: %w[boo far faz],
-      )
-      context.to_h.should eq({
-         7 => "foo",
-         8 => "bar",
-         9 => "baz",
-        10 => "violent offender!",
-        11 => "boo",
-        12 => "far",
-        13 => "faz",
-      })
+      with_foo_context do |context|
+        context.to_h.should eq({
+           7 => "foo",
+           8 => "bar",
+           9 => "baz",
+          10 => "violent offender!",
+          11 => "boo",
+          12 => "far",
+          13 => "faz",
+        })
+      end
     end
   end
 end

src/backtracer/backtrace/frame/context.cr

@@ -15,6 +15,16 @@ module Backtracer
     def initialize(@lineno, @pre, @line, @post)
     end
 
+    # Returns an array composed of context lines from `pre`,
+    # `line` and `post`.
+    def to_a : Array(String)
+      ([] of String).tap do |ary|
+        ary.concat(pre)
+        ary << line
+        ary.concat(post)
+      end
+    end
+
     # Returns hash with context lines, where line numbers are
     # the keys and the lines itself are the values.
     def to_h : Hash(Int32, String)