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m04-zero-cost

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Mastering C++ Polymorphism: Templates, Concepts, and Virtual Functions. Triggers: templates, concepts, vtable, CRTP, static polymorphism, dynamic polymorphism, SFINAE.

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13eholder

13eholder/Modern-Cpp-Skills

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مبرمجو الحاسوبمهن الحاسوب والرياضيات·SOC 15-1251

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SKILL.md

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name	m04-zero-cost
description	Mastering C++ Polymorphism: Templates, Concepts, and Virtual Functions. Triggers: templates, concepts, vtable, CRTP, static polymorphism, dynamic polymorphism, SFINAE.

C++ Zero-Cost Abstractions

Core Question

When do we determine the type?

Compile Time (Static): Templates, Concepts, CRTP. Zero runtime cost, larger binary.
Runtime (Dynamic): Virtual functions, std::any, std::variant. Flexible, vtable overhead.

Error → Design Question

Issue	Design Question
Template spew	Are you missing Concepts constraints?
Linker error	Did you define template in .cpp instead of .h?
Object slicing	Did you assign Derived to Base value?
Slow build	Are you overusing headers/templates?

Thinking Prompt

Is the set of types known at compile time?
- Yes? → Templates or std::variant.
- No? → Inheritance (Virtual functions).
Do I need to store them in a list?
- Homogeneous? → std::vector<T>.
- Heterogeneous? → std::vector<std::unique_ptr<Base>> or std::vector<std::variant<...>>.
Does the interface match exactly?
- Duck typing needed? → Templates (Concepts).
- Strict hierarchy? → Inheritance.

Trace Up / Down

Trace Up:
- Issue: "Virtual function call is too slow in tight loop."
- Cause: Indirect branch misprediction.
- Fix: Switch to Static Polymorphism (CRTP or Templates) if types are known.
Trace Down:
- Intent: "I want a function that accepts anything that has .draw()."
- Code (C++20): void render(Drawable auto& item) { item.draw(); }

Quick Reference

Pattern	Dispatch	Cost	Use When
`virtual`	Dynamic	Vtable + Cache miss	Plugins, Runtime extensions.
Template	Static	Code bloat	High perf, Type deduction.
`std::function`	Dynamic	Alloc + Indirect	Storing callbacks.
`std::variant`	Static branching	Branch switch	Closed set of types.
CRTP	Static	Zero	Static inheritance.

المزيد من هذا المستودع

نفس المستودع

cpp20-skill-creator

13eholder/Modern-Cpp-Skills

Use when creating skills for C++20 standard library features, language constructs, remote third-party libraries, or local C++ projects. Keywords: create C++20 skill, create std skill C++, create concept skill, create local C++ skill, 创建 C++20 skill, 创建标准库技能, 创建 concept 技能, 本地库生成 skill, 动态 C++ skill, skill for ranges, skill for coroutines, skill for concepts, generate C++ skill from local path, C++20 技能, 从文档创建 skill, from docs create C++ skill

2026-02-1414

m01-ownership

13eholder/Modern-Cpp-Skills

Mastering C++ Ownership: Move Semantics, RAII, and Reference Safety. Triggers: std::move, use-after-free, double-free, dangling pointer, copy elision, RVO, reference qualifiers.

2026-01-2514

m02-resource

13eholder/Modern-Cpp-Skills

Mastering C++ Smart Pointers: unique_ptr, shared_ptr, weak_ptr. Triggers: memory management, cycles, enable_shared_from_this, make_unique, make_shared, custom deleters.

2026-01-2514

m03-mutability

13eholder/Modern-Cpp-Skills

Mastering C++ Const Correctness and Mutability. Triggers: const, mutable, logically const, bitwise const, data race, mutex, shared_mutex, thread safety.

2026-01-2514

m05-type-driven

13eholder/Modern-Cpp-Skills

Mastering C++ Type-Driven Design. Triggers: strong types, phantom types, type state pattern, builder pattern, invalid state unrepresentable.

2026-01-2514

m06-error-handling

13eholder/Modern-Cpp-Skills

Mastering C++ Error Handling. Triggers: exceptions, try-catch, noexcept, std::expected, std::optional, error codes, assert, terminate.

2026-01-2514

name	m04-zero-cost
description	Mastering C++ Polymorphism: Templates, Concepts, and Virtual Functions. Triggers: templates, concepts, vtable, CRTP, static polymorphism, dynamic polymorphism, SFINAE.

C++ Zero-Cost Abstractions

Core Question

When do we determine the type?

Compile Time (Static): Templates, Concepts, CRTP. Zero runtime cost, larger binary.
Runtime (Dynamic): Virtual functions, std::any, std::variant. Flexible, vtable overhead.

Error → Design Question

Issue	Design Question
Template spew	Are you missing Concepts constraints?
Linker error	Did you define template in .cpp instead of .h?
Object slicing	Did you assign Derived to Base value?
Slow build	Are you overusing headers/templates?

Thinking Prompt

Is the set of types known at compile time?
- Yes? → Templates or std::variant.
- No? → Inheritance (Virtual functions).
Do I need to store them in a list?
- Homogeneous? → std::vector<T>.
- Heterogeneous? → std::vector<std::unique_ptr<Base>> or std::vector<std::variant<...>>.
Does the interface match exactly?
- Duck typing needed? → Templates (Concepts).
- Strict hierarchy? → Inheritance.

Trace Up / Down

Trace Up:
- Issue: "Virtual function call is too slow in tight loop."
- Cause: Indirect branch misprediction.
- Fix: Switch to Static Polymorphism (CRTP or Templates) if types are known.
Trace Down:
- Intent: "I want a function that accepts anything that has .draw()."
- Code (C++20): void render(Drawable auto& item) { item.draw(); }

Quick Reference

Pattern	Dispatch	Cost	Use When
`virtual`	Dynamic	Vtable + Cache miss	Plugins, Runtime extensions.
Template	Static	Code bloat	High perf, Type deduction.
`std::function`	Dynamic	Alloc + Indirect	Storing callbacks.
`std::variant`	Static branching	Branch switch	Closed set of types.
CRTP	Static	Zero	Static inheritance.