p-groarke/defensive_cpp

C++ Defensive Macros

defensive_cpp

A collection of compile-time validation rules to harden your classes.

Compile-time errors with nice error messages to prevent silently loosing implicitly-declared constructors or default constructors, to enforce the rule of 5, to ensure a type is fast inside a vector, enforce move only, etc.

See Easy Defensive Programming for an introduction to the concept and its beginnings. Easy Defensive Programming - Up To Eleven for a follow-up post about how the library is implemented and its limitations.

Table of contents

• Build Instructions
  • Windows
  • Unixes
• Usage
• Rules and Examples
  • FEA_FULFULLS_RULE_OF_5
    • Example
  • FEA_FULFULLS_5_CTORS
    • Example
  • FEA_FULFULLS_RULE_OF_6
    • Example
  • FEA_FULFULLS_6_CTORS
    • Example
  • FEA_FULFILLS_FAST_VECTOR
    • Example
  • FEA_FULFILLS_MOVE_ONLY
    • Example
  • FEA_FULFILLS_NON_CONSTRUCTIBLE
    • Example

Build Instructions

mkdir build && cd build

Windows

cmake .. -A x64 -DBUILD_TESTING=Off && cmake --build .

or

..\conan.bat && cmake .. -A x64 && cmake --build .

Unixes

cmake .. -DBUILD_TESTING=Off && cmake --build .

or

../conan.sh && cmake .. && cmake --build .

Usage

Include <defensive/defensive.hpp> and apply a rule macro after your class.

struct example {
	~example() {
	}
	example(const example&) {
	}
	example(example&&) {
	}
	example& operator=(const example&) {
	}
	example& operator=(example&&) {
	}
};

FEA_FULFILLS_RULE_OF_5(example);	// Passes

struct example {
	~example() {
	}
	example(const example&) {
	}
	example(example&&) {
	}
	example& operator=(const example&) = default;
	example& operator=(example&&) = default;
};

FEA_FULFILLS_RULE_OF_5(example);	// Fails

/**
 * Failure error messages:
 * - test1 : doesn't fulfill rule of 5
 * - test1 : must implement user-defined move assignement operator
 * - test1 : must implement user-defined copy assignement operator
 */

Rules and Examples

More examples can be found in tests/main.cpp.

FEA_FULFULLS_RULE_OF_5

Makes sure a class fulfulls Rule of 5. All 5 constructors/operators are present (destructor, copy constructor, move constructor, copy assignement operator, move assignement operator). If you implement 1 custom constructor/destructor/operator, you need to implement all of them.

There is a withstanding C++ bug that prevents perfect execution of this rule. If you start by implementing a custom destructor, then it is impossible to detect whether the copy constructor and move constructor are user-defined or generated.

MSVC sometimes has issues, use = default; to fix those.

Example

struct pass {
	int t = 42;
};
FEA_FULFILLS_RULE_OF_5(pass); // PASS

struct fail {
	fail& operator=(const fail&) {}
	
	int t = 42;
};
FEA_FULFILLS_RULE_OF_5(fail); // FAIL

FEA_FULFULLS_5_CTORS

Makes sure 5 constructors/operators are present (destructor, copy constructor, move constructor, copy assignement constructor, move assignement constructor). Useful when using rule of 0 or when using = default.

Example

struct pass {
	int t = 42;
};
FEA_FULFILLS_5_CTORS(pass); // PASS

struct fail {
	fail(const fail&) = delete;
	
	int t = 42;
};
FEA_FULFILLS_5_CTORS(fail); // FAIL

FEA_FULFULLS_RULE_OF_6

Rule of 5 with an extra check to make sure your class has a default constructor. All 6 constructors/operators are present (default constructor, destructor, copy constructor, move constructor, copy assignement operator, move assignement operator). If you implement 1 of 5 custom constructor/destructor/operator, you need to implement all of them (destructor, copy constructor, move constructor, copy assignement operator, move assignement operator).

Example

struct pass {
	int t = 42;
};
FEA_FULFILLS_RULE_OF_6(pass); // PASS

struct fail {
	fail(int) {}
	
	int t = 42;
};
FEA_FULFILLS_RULE_OF_6(fail); // FAIL

FEA_FULFULLS_6_CTORS

Make sure all 6 constructors/operators are present (default, destructor, copy constructor, move constructor, copy assignement operator, move assignement operator). Useful when using rule of 0 or = default.

Example

struct pass {
	int t = 42;
};
FEA_FULFILLS_6_CTORS(pass); // PASS

struct fail {
	fail() = delete;
	
	int t = 42;
};
FEA_FULFILLS_6_CTORS(fail); // FAIL

FEA_FULFILLS_FAST_VECTOR

Ensures your class is optimized to be stored in a vector. Checks whether it is trivially destructible (skips destructor call on resize) and trivially copy constructible (use memcpy on resize). If not, falls back to ensure your class is noexcept move constructible (vector resize cannot use your move constructor if it isn't marked noexcept).

Example

struct pass {
	int t = 42;
};
FEA_FULFILLS_FAST_VECTOR(pass); // PASS

struct fail {
	~fail() {}
	fail(fail&&) {}
	
	int t = 42;
};
FEA_FULFILLS_FAST_VECTOR(fail); // FAIL

FEA_FULFILLS_MOVE_ONLY

Ensures your class is move only. There is no copy constructor and no copy assignement operator. The move constructor and move assignement operator is present.

Example

struct pass {
	pass(const pass&) = delete;
	pass& operator=(const pass&) = delete;
	int t = 42;
};
FEA_FULFILLS_MOVE_ONLY(pass); // PASS

struct fail {
	int t = 42;
};
FEA_FULFILLS_MOVE_ONLY(fail); // FAIL

FEA_FULFILLS_NON_CONSTRUCTIBLE

Ensures your class is non constructible, aka had no default constructor, destructor, copy constructor, move constructor, copy assignement operator and move assignement operator. Useful when writing static singleton classes.

Example

struct pass {
	pass() = delete;
	~pass() = delete;
	pass(const pass&) = delete;
	pass(pass&&) = delete;
	pass& operator=(const pass&) = delete;
	pass& operator=(pass&&) = delete;
	int t = 42;
};
FEA_FULFILLS_NON_CONSTRUCTIBLE(pass); // PASS

struct fail {
	int t = 42;
};
FEA_FULFILLS_NON_CONSTRUCTIBLE(fail); // FAIL