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Narrow a union

YOUR TASK

Make this happen

3 steps

  1. A union admits more than one shape. Use type(value) to distinguish text from numbers, then return a number on both paths.

  2. Read the cases in lesson.test.lua, then choose Check solution to see what needs to change.

  3. Update subject.lua until every test passes. Keep the supplied tests unchanged.

Start with Check solution, then use the failures to guide your edits.

Read the starter and tests

subject.lua

exports.asNumber = function(value: number | string): number
  return value
end

lesson.test.lua

local t = require("test")
local subject = require("cococo.subject")
t.it("preserves numbers", function()
  local s = subject.load()
  t.expect(s.asNumber(12)):eq(12)
end)
t.it("parses text", function()
  local s = subject.load()
  t.expect(s.asNumber("12")):eq(12)
end)
t.it("invalid text defaults", function()
  local s = subject.load()
  t.expect(s.asNumber("x")):eq(0)
end)