模式匹配与控制流
掌握 Elixir 强大的模式匹配功能，以及 `if`、`case` 和 `cond` 等基本控制流结构。
模式匹配与控制流 是 CoddyKit 上的免费 Elixir & Phoenix: Scalable Backend Development 课时。 这是第 3 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Elixir & Phoenix: Scalable Backend Development 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Elixir & Phoenix: Scalable Backend Development 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
Intro to Pattern Matching
Pattern matching is the heart of Elixir. Here = is a match operator, not assignment — it makes the left side equal the right.
Basic Variable Matching
The simplest match binds an unbound variable to a value. If it is already bound, Elixir instead checks that the two sides actually match.
defmodule BasicMatchDemo do
def run do
# 'a' is unbound, so it's assigned 10
a = 10
IO.puts "a is: #{a}"
# 'b' is unbound, so it's assigned 20
b = 20
IO.puts "b is: #{b}"
# This matches 'a' to the value of 'b' (20)
# 'a' is re-bound to 20
a = b
IO.puts "After a = b, a is: #{a}"
end
end
BasicMatchDemo.run()Matching with Literals
Put a literal on the left and the match becomes an assertion: it succeeds only if both sides are equal, otherwise it raises. Handy for validation.
defmodule LiteralMatchDemo do
def run do
# This matches because 1 is equal to 1
1 = 1
IO.puts "1 = 1 matched successfully!"
# This matches because 'hello' is equal to 'hello'
"hello" = "hello"
IO.puts "'hello' = 'hello' matched successfully!"
# If you uncomment the line below, it will cause a MatchError
# 1 = 2
# IO.puts "This line would not be reached if 1 = 2 failed"
end
end
LiteralMatchDemo.run()Deconstructing Tuples
Matching shines on tuples — deconstruct them straight into variables, which is exactly how you unpack {:ok, value} results.
defmodule TupleMatchDemo do
def run do
# Match a tuple to extract its elements
{:person, name, age} = {:person, "Alice", 30}
IO.puts "Name: #{name}, Age: #{age}"
# Match a common result tuple
{:ok, data} = {:ok, "User fetched successfully"}
IO.puts "Status: ok, Data: #{data}"
# If you uncomment the line below, it will cause a MatchError
# {:error, reason} = {:ok, "Success"}
end
end
TupleMatchDemo.run()Deconstructing Lists
Deconstruct lists with the [head | tail] pattern: head is the first element, tail the rest. Use _ for parts you do not care about.
defmodule ListMatchDemo do
def run do
list = [1, 2, 3, 4, 5]
# Match head and tail
[head | tail] = list
IO.puts "Head: #{head}, Tail: #{inspect tail}"
# Match specific elements
[first, second, third | _rest] = list
IO.puts "First: #{first}, Second: #{second}, Third: #{third}"
# Match an empty list
[] = []
IO.puts "Empty list matched!"
end
end
ListMatchDemo.run()The Pin Operator (^)
The pin operator ^ says "do not rebind — match against this variable's current value" instead. Great for asserting equality.
defmodule PinOperatorDemo do
def run do
value_a = 10
value_b = 10
# This uses the current value of value_a (10) to match against value_b
# It succeeds because 10 matches 10
^value_a = value_b
IO.puts "Match successful: value_a = #{value_a}, value_b = #{value_b}"
value_c = 5
# If you uncomment the line below, it will cause a MatchError
# because ^value_a (10) is not equal to value_c (5)
# ^value_a = value_c
# IO.puts "This line would not be reached if ^value_a = value_c failed"
end
end
PinOperatorDemo.run()Simple Conditionals: if/unless
For simple branches use if and its mirror unless, each with an optional else. The cleanest tool for one true/false condition.
defmodule IfUnlessDemo do
def run do
number = 7
if number > 5 do
IO.puts "Number is greater than 5"
else
IO.puts "Number is 5 or less"
end
unless rem(number, 2) == 0 do
IO.puts "Number is odd"
else
IO.puts "Number is even"
end
end
end
IfUnlessDemo.run()Handling Multiple Patterns with case
The case expression matches one value against several patterns and runs the first that fits — pattern matching as control flow.
defmodule CaseExpressionDemo do
def run do
status = {:ok, "Data loaded"}
case status do
{:ok, message} ->
IO.puts "Success: #{message}"
{:error, reason} ->
IO.puts "Failed: #{reason}"
_ ->
IO.puts "Unknown status"
end
# Another example with a simple value
grade = "B"
case grade do
"A" -> IO.puts "Excellent!"
"B" -> IO.puts "Good job!"
_ -> IO.puts "Keep trying!"
end
end
end
CaseExpressionDemo.run()Multiple Conditions with cond
When you have many boolean checks (an if/else-if chain elsewhere), cond runs the first clause whose condition is true.
defmodule CondExpressionDemo do
def run do
score = 85
cond do
score >= 90 -> IO.puts "Grade: A"
score >= 80 -> IO.puts "Grade: B"
score >= 70 -> IO.puts "Grade: C"
true -> IO.puts "Grade: D or lower" # The 'true' clause acts as a catch-all
end
temperature = 25
cond do
temperature > 30 -> IO.puts "It's hot!"
temperature > 20 -> IO.puts "It's warm."
true -> IO.puts "It's cool."
end
end
end
CondExpressionDemo.run()Pattern Matching Challenge
Consider the following Elixir code snippet:
data = ["apple", {:fruit, "banana"}, "cherry"]
[first, {:fruit, second}, _] = dataWhat will be the final values of the variables first and second after this code executes?
Recap: Pattern Matching & Control
Recap: = matches, you deconstruct tuples and lists, ^ pins a value, and if/case/cond drive your control flow.
常见问题解答
「模式匹配与控制流」课时是免费的吗？
是的 — 「模式匹配与控制流」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Elixir & Phoenix: Scalable Backend Development 课程的其余内容，请升级到 CoddyKit PRO。 Elixir & Phoenix: Scalable Backend Development 课程共包含 4 节课。
「模式匹配与控制流」这节课中我会学到什么？
掌握 Elixir 强大的模式匹配功能，以及 `if`、`case` 和 `cond` 等基本控制流结构。 你通过在浏览器中直接运行的动手代码来练习 Elixir & Phoenix: Scalable Backend Development，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 Elixir & Phoenix: Scalable Backend Development 需要有经验吗？
无需任何先前经验。CoddyKit 上的 Elixir & Phoenix: Scalable Backend Development 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 3 节课，共 4 节。
「模式匹配与控制流」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 Elixir & Phoenix: Scalable Backend Development 课中编写并运行代码吗？
能。每节 Elixir & Phoenix: Scalable Backend Development 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。