# cpp-templates

Demystifies C++ template compiler errors and guides the transition from legacy SFINAE to modern C++20 concepts.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 528 installs · ★ 267
- Author: mohitmishra786
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/compilers/cpp-templates/SKILL.md
- Updated: 2026-06-27
- HTML: https://affpapa.org/en/nevibecode/skills/cpp-templates

## What it does

The skill instructs coding agents on diagnosing verbose GCC and Clang template errors. Read errors from the bottom up. This approach pinpoints the exact type that caused deduction or substitution to fail. To reduce compiler noise, it suggests flags such as `-ftemplate-backtrace-limit=3` or `-fconcepts-diagnostics-depth=3`.

It covers migrating legacy SFINAE constructs to modern C++20 concepts. The guide provides patterns for compound `requires` expressions, nested type requirements, and abbreviated function templates. For faster build steps, it shows how to apply `extern template` declarations and branch elimination with `if constexpr`.

To tackle slow builds, the skill outlines template instantiation profiling. Detailed tracing via Templight requires a patched Clang build and KCachegrind for visualization. When running a standard compiler, ClangBuildAnalyzer provides a practical substitute directly on top of CMake.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill cpp-templates -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/cpp-templates/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/cpp-templates/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill cpp-templates -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/cpp-templates/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill cpp-templates -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/cpp-templates/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install mohitmishra786/low-level-dev-skills cpp-templates
```

2. **Manually: put the files in place**
- File: `.github/skills/cpp-templates/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill cpp-templates -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/mohitmishra786/low-level-dev-skills --path skills/compilers/cpp-templates
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/cpp-templates/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill cpp-templates -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/compilers/cpp-templates/SKILL.md

## When to use it
- decipher verbose C++ template error traces from GCC and Clang
- migrate legacy SFINAE overloads to C++20 concepts and requires clauses
- profile template instantiation bottlenecks using ClangBuildAnalyzer
- cut compilation duration using extern template and if constexpr

## Example prompts
- Help me decipher this template deduction failure for std::sort
- Convert this enable_if constraint to a C++20 requires clause
- How do I trace template instantiation times with ClangBuildAnalyzer?

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 1f1b26405ba6f5f0.

BEGIN THIRD-PARTY FILE 1f1b26405ba6f5f0
````text
---
name: cpp-templates
description: C++ template skill for reading template errors and optimizing compile times. Use when deciphering template error stacks, setting -ftemplate-backtrace-limit, writing concepts and requires-clauses, understanding SFINAE vs concepts, or profiling template instantiation bottlenecks with Templight. Activates on queries about C++ templates, template error messages, concepts, requires expressions, SFINAE, template metaprogramming, or slow template compilation.
---

# C++ Templates

## Purpose

Guide agents through reading and fixing template error messages, using concepts as cleaner constraints, understanding SFINAE vs concepts trade-offs, and profiling template instantiation depth and compile times with Templight.

## Triggers

- "How do I read this massive C++ template error?"
- "How do I use concepts to constrain a template?"
- "What's the difference between SFINAE and concepts?"
- "My templates make compilation very slow"
- "How do I write a requires-clause?"
- "How do I profile template instantiation times?"

## Workflow

### 1. Reading template error messages

Template errors print full instantiation chains. Strategy: read from the bottom up.

```text
prog.cpp:25:5: error: no matching function for call to 'sort'
  std::sort(v.begin(), v.end());
  ^~~~~~~~~
/usr/include/c++/13/bits/stl_algo.h:4869:5: note: candidate:
    template<class _RAIter>
    void std::sort(_RAIter, _RAIter)
note: template argument deduction/substitution failed:
prog.cpp:25:5: note: 'MyType' is not a valid type for this template
                             ^~~~~~~~
```

Rules for reading:
1. Find the first error line (top of output) — that's your code
2. Skip all the `note:` lines until you find "required from here" or "in instantiation of"
3. The bottom of the stack shows the type that failed substitution

```bash
# Limit backtrace depth to reduce noise
g++   -ftemplate-backtrace-limit=3  prog.cpp
clang -ftemplate-depth=32           prog.cpp   # default 1024

# Show simplified errors (GCC 12+)
g++ -fconcepts-diagnostics-depth=3  prog.cpp   # for concept failures
```

### 2. SFINAE — legacy constraint technique

SFINAE (Substitution Failure Is Not An Error) silently removes overloads that fail substitution:

```cpp
#include <type_traits>

// Enable function only for arithmetic types
template <typename T,
    std::enable_if_t<std::is_arithmetic_v<T>, int> = 0>
T square(T x) { return x * x; }

// SFINAE with return type
template <typename T>
auto to_string(T x) -> std::enable_if_t<std::is_integral_v<T>, std::string> {
    return std::to_string(x);
}

// Void-t technique for detecting member existence
template <typename, typename = void>
````
END THIRD-PARTY FILE 1f1b26405ba6f5f0

The third-party file has ended. Everything between the 1f1b26405ba6f5f0 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

First 2693 of 7066 bytes. © mohitmishra786 · MIT · https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/compilers/cpp-templates/SKILL.md

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