Introduction to lambdas #25

mcmlevi · 2025-04-02T21:08:00Z

A tutorial explaining lambdas. This touches upon what a lambda is and what the structure is like.

A tutorial explaining lambdas.

eisenwave · 2025-04-02T21:10:17Z

src/resources/cpp/lambdas.md

+
+## What is a lambda?
+
+Lambdas are similar to function, however they are not identical they specifically are [closures](https://en.wikipedia.org/wiki/Closure_(computer_programming)) what might be a term you are familiar with from other languages.


"function" should be plural, and there are a few English mistakes here.

eisenwave · 2025-04-02T21:19:19Z

src/resources/cpp/lambdas.md

+
+Lambdas are similar to function, however they are not identical they specifically are [closures](https://en.wikipedia.org/wiki/Closure_(computer_programming)) what might be a term you are familiar with from other languages.
+
+if they are similar to functions one might ask why would I ever need a lambda? They have multiple usages but the simplest and most common one is for predicates in algorithms. Algorithms are nice and generic and you want their behavior to be slightly different depending on your specific use case.


Name-dropping "predicates" may be a bit demanding. This is mathematical lingo.

In general, I think this article needs a strong motivating example as early as possible, prior to any lingo. Something like:

For example, algorithms in the standard library can often have their behavior changed using something callable. Creating a whole function is often excessive, and we use lambdas instead:

int non_a_amount = std::ranges::count_if("abcaabbac", [](char c) { return c != 'a'; });

Hmmm, I think that could indeed be reworded with less complicated wording.

I did try to make a motivator immediately after this as well, but I agree it could definitely pull a stronger example forward at the very start.

Allright I tried to update a bit, and hopefully this should be a bit better now.

src/resources/cpp/lambdas.md

Co-authored-by: Jan Schultke <[email protected]>

…o lambda_tutorial

src/resources/cpp/lambdas.md

Removed fluff, added return 0 in main.

…o lambda_tutorial

As per Eisenwave's suggestion, an attempt to create a stronger use case at the start.

src/resources/cpp/lambdas.md

nickclark2016 · 2025-04-11T23:57:26Z

src/resources/cpp/lambdas.md

+Lambdas are similar to functions, however they are not identical they specifically are
+[closures](<https://en.wikipedia.org/wiki/Closure_(computer_programming)>).
+
+if they are similar to functions one might ask why would I ever need a lambda? For example, algorithms in the standard


I think we should leave discussion on "when to use lambdas" to after they have been discussed more thoroughly. I also don't like the voice of "why would I ever need a lambda?". I would rather see a direct discussion of when to use lambdas versus when to use functions without "I" or "you" pronouns.

nickclark2016 · 2025-04-12T00:00:08Z

src/resources/cpp/lambdas.md

+
+`int non_a_amount = std::ranges::count_if("abcaabbac", [](char c) { return c != 'a'; });`
+
+This counts all results where the lambda returns true, in this case if the latter is not 'a'.


I would suggest focusing more on the lambda first, then bringing in things like ranges/algorithms. Here, you're introducing two new concepts: lambdas and a range algorithm. I would just provide a name lambda, discuss what the lambda is, then pass it to the range algo and describe how the two interact.

I updated this code sample a bit and introduced a simpler code example first. @nickclark2016 is this better for you?

src/resources/cpp/lambdas.md

nickclark2016 · 2025-04-12T00:07:14Z

src/resources/cpp/lambdas.md

+
+### Capture list
+
+As the name implies, the capture list allows us to capture values into the lambda as it's constructed. Unlike the


Tweak on wording: "capture value into the lambda where it is defined". Constructed feels a bit weird in the context of a lambda.

As the name implies, the capture list allows us to capture values as the lambda is constructed.

Hopefully that's better.

nickclark2016 · 2025-04-12T00:09:22Z

src/resources/cpp/lambdas.md

+
+### body `{}`
+
+The lambda body is the exact same as the body of the function. It's hold the code that the lambda will execute when it's


Reword: It holds the code code that the lambda will execute when it is invoked.

The body contains all the code that will be executed when the lambda is invoked.

Is that better?

src/resources/cpp/lambdas.md

nickclark2016 · 2025-04-12T00:12:49Z

src/resources/cpp/lambdas.md

General voice comment: Consider moving "we" and "you" to the specific part of the code whenever possible.

I took a closer look at this, and wow, do I use this pattern a lot. I looked at the entire file and tried to address the wording a lot to use a more passive style. This should also be more fitting for the intended purpose, I feel.

nickclark2016 · 2025-04-12T00:14:11Z

src/resources/cpp/lambdas.md

Please check spelling, capitalization, and contractions across the whole file.

* update article on UB * Avoid wrapping without sacrificing formatting --------- Co-authored-by: Jeremy Rifkin <[email protected]>

nickclark2016 · 2025-05-01T12:17:35Z

src/resources/cpp/lambdas.md

+// A lambda that checks if the passed in letter is not equal to a.
+auto a_checker = [](char c) {
+    return c != 'a';
+    };


Consistency: }; should not be indented

nickclark2016 · 2025-05-01T12:19:00Z

src/resources/cpp/lambdas.md

+}
+```
+
+As is visible above have noticed that the lambda uses the same variable name inside the lambda as declared in main.


Reword this sentence please. It does not flow well.

nickclark2016 · 2025-05-01T12:22:39Z

src/resources/cpp/lambdas.md

+};
+```
+
+Here a copy is made of multiply_number called num. The type does not need to be specified here.


Suggested Reword:

Here, a copy of multiply_number is made and assigned to num. Notice that the type is not specified here.

nickclark2016 · 2025-05-01T12:24:10Z

src/resources/cpp/lambdas.md

+
+Here a copy is made of multiply_number called num. The type does not need to be specified here.
+
+Making a copy of a value might be undesirable and thus it's also possible to capture the variable as a reference. Now no


Reword second sentence to say "Now, multiply_number is being taken by reference instead of by copy."

nickclark2016 · 2025-05-01T12:27:45Z

src/resources/cpp/lambdas.md

+    return n * multiply_number;
+};
+```
+


Just a question (no action needed necessarily) - Should we talk about capture by reference and note how people need to be careful when using capture by reference/be aware of the lifetime implications (i.e. your lambda may have an invalid reference if the original object has its lifetime end before the lambda's lifetime ends)

nickclark2016 · 2025-05-01T12:29:57Z

src/resources/cpp/lambdas.md

+```cpp
+#include <iostream>
+
+void say_a()


Consistency: Braces are same line, single space between () and {. Please fix across the entire document.

jeremy-rifkin · 2025-07-12T20:47:36Z

Converting to draft until ready

Initial lambda draft

bdd0a5e

A tutorial explaining lambdas.

eisenwave suggested changes Apr 2, 2025

View reviewed changes

mcmlevi and others added 5 commits April 3, 2025 00:01

lambda parts surgestion

50dda00

Co-authored-by: Jan Schultke <[email protected]>

text fixes

064d04c

Co-authored-by: Jan Schultke <[email protected]>

typos and lambda spacing

419cd21

Merge branch 'lambda_tutorial' of https://github.com/mcmlevi/wiki int…

406527d

…o lambda_tutorial

fixed incorrect info regarding omiting of lambda parameters.

6358257

nickclark2016 requested changes Apr 2, 2025

View reviewed changes

mcmlevi added 7 commits April 3, 2025 09:47

Feedback

2521400

Removed fluff, added return 0 in main.

run auto formatter

b954807

use bound lambda argument rather then orginal

81e9252

removed prereq

7f7e9d1

Merge branch 'lambda_tutorial' of https://github.com/mcmlevi/wiki int…

b1eac3a

…o lambda_tutorial

added trailing return type information

1d7bd66

Attempt at making a stronger entry point for lambdas

c2fd62d

As per Eisenwave's suggestion, an attempt to create a stronger use case at the start.

nickclark2016 requested changes Apr 12, 2025

View reviewed changes

mcmlevi added 3 commits April 24, 2025 19:02

adressing code style / tone comments.

384595c

Simpler lambda introduction

55e3b75

tonal changes

f6be794

jeremy-rifkin added a commit that referenced this pull request Apr 30, 2025

Update article on UB (#25)

ba21107

* update article on UB * Avoid wrapping without sacrificing formatting --------- Co-authored-by: Jeremy Rifkin <[email protected]>

nickclark2016 requested changes May 1, 2025

View reviewed changes

jeremy-rifkin marked this pull request as draft July 12, 2025 20:47


		## What is a lambda?

		Lambdas are similar to function, however they are not identical they specifically are [closures](https://en.wikipedia.org/wiki/Closure_(computer_programming)) what might be a term you are familiar with from other languages.


		Lambdas are similar to function, however they are not identical they specifically are [closures](https://en.wikipedia.org/wiki/Closure_(computer_programming)) what might be a term you are familiar with from other languages.

		if they are similar to functions one might ask why would I ever need a lambda? They have multiple usages but the simplest and most common one is for predicates in algorithms. Algorithms are nice and generic and you want their behavior to be slightly different depending on your specific use case.


		`int non_a_amount = std::ranges::count_if("abcaabbac", [](char c) { return c != 'a'; });`

		This counts all results where the lambda returns true, in this case if the latter is not 'a'.


		### Capture list

		As the name implies, the capture list allows us to capture values into the lambda as it's constructed. Unlike the


		### body `{}`

		The lambda body is the exact same as the body of the function. It's hold the code that the lambda will execute when it's


		Here a copy is made of multiply_number called num. The type does not need to be specified here.

		Making a copy of a value might be undesirable and thus it's also possible to capture the variable as a reference. Now no

Introduction to lambdas #25

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mcmlevi commented Apr 2, 2025

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mcmlevi Apr 2, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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jeremy-rifkin commented Jul 12, 2025

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mcmlevi Apr 2, 2025 •

edited

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