init cpp repo

.clang-format

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+---
+Language: Cpp
+BasedOnStyle: Google
+...

.clangd

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+CompileFlags:
+  Add:
+    - -Xclang
+    - -fno-validate-pch
+    - -fretain-comments-from-system-headers
+  Compiler: clang++
+Index:
+  Background: true
+Diagnostics:
+  ClangTidy:
+    Add:
+      - modernize-*
+      - performance-*
+      - cppcoreguidelines-*
+    ClangTidyChecks: true
+    Options:
+      UseChecks:
+        - "*"
+      WarningAsErrors: cppcoreguidelines-*
+InlayHints:
+  Enabled: true
+  ParameterNames: true
+  DeducedTypes: true
+  Designators: true
+Completion:
+  AllScopes: true
+SemanticTokens:
+  Enabled: true

.envrc

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+watch_file ./flake.*
+
+use flake

.gitignore

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+/.direnv/
+/build/
+/.cache/
+/compile_commands.json

Makefile

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+.RECIPEPREFIX = >
+.DEFAULT_GOAL = build/main.out
+CXX = clang++
+CXXFLAGS += -std=c++26 -Wno-experimental-header-units
+LDFLAGS += -std=c++26
+SYSTEMHEADER_FLAGS = -Wno-deprecated-builtins -Wno-pragma-system-header-outside-header -Wno-keyword-compat
+build_module_path = $(let first rest,$1,$(if $(rest),-fmodule-file=$(first) $(call build_module_path,$(rest)),-fmodule-file=$(first)))
+
+build/main.out: build/main.o
+> $(CXX) $(LDFLAGS) $^ -o $@
+
+build/main.o: main.cxx build/print.pcm build/type_traits.pcm
+> $(CXX) $(CXXFLAGS) -c $(filter-out %.pcm,$^) $(call build_module_path,$(filter %.pcm,$^))
+> @mv $(patsubst build/%,%,$@) $@
+
+build/%.pcm:
+> $(CXX) $(CXXFLAGS) -xc++-system-header --precompile $(patsubst build/%.pcm,%,$@) -o $@ $(SYSTEMHEADER_FLAGS)
+
+.PHONY: clean run
+clean:
+> @-rm -rf ./build/*
+bear: clean
+> bear -- $(MAKE)
+
+run: $(.DEFAULT_GOAL)
+> @./$(.DEFAULT_GOAL)

flake.lock

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+{
+  "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "id": "flake-utils",
+        "type": "indirect"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1745377448,
+        "narHash": "sha256-jhZDfXVKdD7TSEGgzFJQvEEZ2K65UMiqW5YJ2aIqxMA=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "507b63021ada5fee621b6ca371c4fca9ca46f52c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-cmake": {
+      "locked": {
+        "lastModified": 1745570837,
+        "narHash": "sha256-8MwKbng4lvA5wgBbOx0+VohonuMnUd62xJ6gE4tdXdU=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "ceecbb5d1184da5866a824b7accbb4a8c07a73eb",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "pull/394444/head",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-gcc15": {
+      "locked": {
+        "lastModified": 1745644951,
+        "narHash": "sha256-Rqnc3VvR2T6vJ2JwXhX6h9zwSYjWITk3YdOUKcCM284=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "281c0c16c9c6e2e44e78334f55bbd43dc51c0d70",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "pull/401948/head",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs",
+        "nixpkgs-cmake": "nixpkgs-cmake",
+        "nixpkgs-gcc15": "nixpkgs-gcc15"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

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+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    nixpkgs-gcc15.url = "github:NixOS/nixpkgs/?ref=pull/401948/head";
+    nixpkgs-cmake.url = "github:NixOS/nixpkgs/?ref=pull/394444/head";
+  };
+  outputs =
+    {
+      nixpkgs-cmake,
+      nixpkgs-gcc15,
+      nixpkgs,
+      flake-utils,
+      ...
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        inherit
+          (import nixpkgs-cmake {
+            inherit system;
+            config = {
+              cudaSupport = true;
+            };
+          })
+          cmake
+          ;
+        inherit
+          (import nixpkgs-gcc15 {
+            inherit system;
+            config = {
+              cudaSupport = true;
+            };
+          })
+          gcc15
+          gcc15Stdenv
+          ;
+        pkgs = import nixpkgs {
+          inherit system;
+          config = {
+            cudaSupport = true;
+          };
+        };
+      in
+      {
+        devShells.default =
+          pkgs.mkShell.override
+            {
+              stdenv = pkgs.llvmPackages_20.libcxxStdenv;
+              # stdenv = gcc15Stdenv;
+            }
+            {
+              packages = with pkgs; [
+                llvmPackages_20.clang-tools
+                gnumake
+                llvmPackages_20.clang
+                bear
+                # cmake
+                # gcc15
+              ];
+            };
+      }
+    );
+}

main.cxx

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+import <print>;
+import <type_traits>;
+
+template <bool param1 = false, bool param2 = false>
+struct Builder;
+template <bool enabled>
+struct BuildMixin {};
+
+template <>
+struct BuildMixin<true> {
+  auto build(this auto&& self) { return self.p1 + self.p2; }
+};
+
+template <bool enabled>
+struct Param1Mixin {};
+
+template <>
+struct Param1Mixin<false> {
+  auto fill_param1(this auto&& self) {
+    self.p1 = 1;
+    return Builder<true, std::remove_reference_t<decltype(self)>::param2_v>(
+        self);
+  }
+};
+
+template <bool enabled>
+struct Param2Mixin {};
+
+template <>
+struct Param2Mixin<false> {
+  auto fill_param2(this auto&& self) {
+    self.p2 = 1;
+    return Builder<std::remove_reference_t<decltype(self)>::param1_v, true>(
+        self);
+  }
+};
+
+template <bool param1, bool param2>
+struct Builder : BuildMixin<param1 && param2>,
+                 Param1Mixin<param1>,
+                 Param2Mixin<param2> {
+  const constinit static auto param1_v = param1;
+  const constinit static auto param2_v = param2;
+  int p1;
+  int p2;
+  Builder() : p1(0), p2(0) {}
+  Builder(auto&& other) : p1(other.p1), p2(other.p2) {}
+};
+
+auto main() -> int {
+  Builder builder;
+  auto ret = builder.fill_param1().fill_param2().build();
+  std::println("{}", ret);
+}