Advanced · Module 9 · Lesson 4 of 7
Concepts and Constraints: Requirements That Read Like English
Replace fifty-line template errors with a named C++20 concept, constrain max_of and Pair with requires clauses, and read diagnostics in one line.
By the end you can
- Write a concept that names the operations a template needs
- Constrain function and class templates with requires clauses
- Predict diagnostics when Book lacks ordering or printing
Builds on Specialization: Customizing for One Type.
01 · A question first
You call max_of on two Book records and the compiler emits fifty lines about operator less inside template internals. Which requirement failed, where is it documented, and how could one English sentence at the template boundary have reported it instead?
Make a guess before you read on.
02 · The idea
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What's inside
- Start with the problem
- How the idea works
- A second runnable example
- Why it is correct
- What it costs
- Pitfalls and variations
- Where it is used
03 · Practice
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