Component bslmf_assert [Package bslmf]

Provide a compile-time assertion facility. More...

Classes
struct	BSLMF_COMPILE_TIME_ASSERTION_FAILURE< true >
Namespaces
namespace	bslmf
Defines
#define	BSLMF_ASSERT_CAT(X, Y)   BSLMF_ASSERT_CAT_IMP1(X, Y)
#define	BSLMF_ASSERT_CAT_IMP1(X, Y)   BSLMF_ASSERT_CAT_IMP2(X, Y)
#define	BSLMF_ASSERT_CAT_IMP2(X, Y)   X##Y
#define	BSLMF_ASSERT(expr)

---

Detailed Description

Outline

• Purpose
• Classes
• Macros
• Description

Purpose:

Provide a compile-time assertion facility.

Classes:

Macros:

BSLMF_ASSERT

compile-time assert macro

Description:

This component defines a macro that will generate a compile-time error if its constant integral expression argument evaluates to false (i.e., a value of 0). The BSLMF_ASSERT macro is similar to the standard run-time assert macro, except that its argument is evaluated at compile-time, it produces no executable code, and it can be used safely in header files.

  BSLMF_ASSERT(sizeof(int) >= sizeof(char));    // OK
  BSLMF_ASSERT(sizeof(double) < sizeof(char));  // COMPILE ERROR!

The second line will result in a compile error with a message stating that the type BSLMF_COMPILE_TIME_ASSERTION_FAILURE is incomplete, usually preceded by the file and line number where the macro was used. The following error message is typical of most compilers:

  $ CC -g myfile.cpp
  "myfile.cpp", line 86: Error: The type
  "BSLMF_COMPILE_TIME_ASSERTION_FAILURE<0>" is incomplete.
  1 Error(s) detected.

If the macro argument is true, the macro will generate an innocuous typedef with a name that is the concatenation of the symbol bslmf::Assert, and the value of __LINE__ (which will be the line number in the file where the macro was called). For example, the first line from the example above might result in the following statement:

  typedef bslmf::AssertTest<1> bslmf_Assert_85;

Note that these generated typedefs are implementation details of the compile-time checking facility and are not intended to be used directly outside of this component.

Attempting to invoke BSLMF_ASSERT on a non-compile-time value will typically result in a compilation error.

BSLMF_ASSERT can be used at namespace, class, and function scope to assert compile-time conditions. WARNING: a compiler bug on certain platforms produces an error when the BSLMF_ASSERT macro is used more than once on the same line in class scope.

  +---------------------------------------------
  | // mytype.h
  | #ifndef INCLUDED_BSLMF_ASSERT
  | #include <bslmf_assert.h>
  | #endif
  |
  | class MyType {
  |     BSLMF_ASSERT(sizeof(int) >= sizeof(char));  // OK
  |     BSLMF_ASSERT(sizeof(int) >= sizeof(char));  // OK
  |     BSLMF_ASSERT(1 == 1);                       // OK
  |     BSLMF_ASSERT(1 == 1); BSLMF_ASSERT(1 == 1); // SAME LINE - MIGHT
  |                                                 // CAUSE ERROR!
  |
  |     int d_data;
  |     ...
  |     void foo();
  |     ...
  | };

        +---------------------------------------------
        | // mytype.cpp
        | #include <mytype.h>
        | #include <bslmf_assert.h>
        |
        | BSLMF_ASSERT(sizeof(int) >= sizeof(char));
        |
        | void MyType::foo()
        | {
        |     BSLMF_ASSERT(sizeof(int) >= sizeof(char));
        |     ...
        | }

---

Define Documentation

#define BSLMF_ASSERT_CAT	(		X,
			Y
	)			BSLMF_ASSERT_CAT_IMP1(X, Y)

#define BSLMF_ASSERT_CAT_IMP1	(		X,
			Y
	)			BSLMF_ASSERT_CAT_IMP2(X, Y)

#define BSLMF_ASSERT_CAT_IMP2	(		X,
			Y
	)			X##Y

#define BSLMF_ASSERT

(

expr

)

Value:

BSLA_MAYBE_UNUSED typedef BloombergLP::bslmf::AssertTest<                     \
         sizeof(BloombergLP::BSLMF_COMPILE_TIME_ASSERTION_FAILURE<!!(expr)>)> \
                                    BSLMF_ASSERT_CAT(bslmf_Assert_, __LINE__)