deeplearning4j--deeplearning4j/libnd4j/dev-docs/Helpers.md

Helpers

Requirements Helper

Requirements helper was introduced to replace plain checks for making them output informative messages (Debug and Verbose mode) and also replace macros REQUIRE_TRUE.

• it will lazily evaluate values and messages if the type wrapped and has getValue and getMsg methods
• it is implicit bool. this makes it usable with logical operators and also inside if conditions. Besides it will benefit from shortcircuit nature of those operators.
• it has the following check methods

Requirements& expect(const T& expVar,const T1& reqVar, Op comparison, const char *first_half="")
Requirements& expectEq(const T& exp,const T1& req)
Requirements& expectNotEq(const T& exp,const T1& req)
Requirements& expectLess(const T& exp,const T1& req)
Requirements& expectLessEq(const T& exp,const T1& req)
Requirements& expectGreater(T exp, T1 req)
Requirements& expectGreaterEq(const T& exp,const T1& req
Requirements& expectTrue(const T& expVar, const char *msg=)
Requirements& expectFalse(const T& expVar, const char *msg=)

• you can either log the success case or throw error on the failure
• it can use plain types for checks.
• if value has stream operator it will be used to output its value. for custom types you may need add that by yourself ostream& operator<<(ostream& os, const CustomUserType& dt)
• there is generic template InfoVariable wrapper for types to make it informative. you can use lambda operators with them as well to make it lazily evaluated
• we added custom ShapeInfoVariable wrapper for the NDArray and vector<> shapes to make them informative
• one can use expect to add its own proper comparison. simple lambda for that will be like this:

[](const decltype(expType)& l, const decltype(reqType)& r){
            //compare and return
            return  ....;
        }

Examples:

firstly, we should enable logging

    sd::Environment::getInstance().setDebug(true);
    sd::Environment::getInstance().setVerbose(true); 

1. simple case

Requirements req1("Requirement Helper Example#1");
int x = 20;
req1.expectLess(x, 22);
req1.expectEq(x, 21); //should fail

Output: Requirement Helper Example#1: {20} expected to be equal to 21

2. using InfoVariable wrapper

int age = 15;
Requirements req2("Requirement Helper Example#2");
req2.expectGreaterEq(makeInfoVariable(age, "the user's age"), 18);

Output:

Requirement Helper Example#2: the user's age {15} expected to be greater than or equal  18

3. helper behavior while using many checks in one block

int getAge(){
    std::cout<<"getAge() was called"<<std::endl;
    return 15;
}
....
Requirements req3("Requirement Helper Example#3");
int z = 20;
req3.expectEq(z, 21); 
req3.expectGreaterEq(makeInfoVariable(getAge(), "the user's age"), 18);

Output:

Requirement Helper Example#3:  {20} expected to be equal to  21
getAge() was called

As it is seen the second check did not happen as the previous failed. But still getAge() method was called as its function argument.

4. using shortcircuit to avoid Requirement call at all if the previous one was failed

Requirements req4("Requirement Helper Example#4");
int zz = 20;
req4.expectEq(zz, 21) &&  //shortcircuit And
req4.expectGreaterEq(makeInfoVariable(getAge(), "the user's age"), 18);

Output:

Requirement Helper Example#4:  {20} expected to be equal to  21

5. using lambdas with InfoVariable. it will make it lazily evaluated

Requirements req5("Requirement Helper Example#5"); 
req5.expectEq( 21, 
            makeInfoVariable(21, []{
                   std::cout<<"lambda call#1"<<std::endl;
                   return "twenty one";
               }));
req5.expectEq(makeInfoVariable([]{ return 20;}, []{return "twenty";}), 
               makeInfoVariable(21, []{
                   std::cout<<"lambda call#2"<<std::endl;
                   return "twenty one";
               }));
req5.expectGreaterEq(makeInfoVariable([]{
                        std::cout<<"lambda call#3" <<std::endl;
                        return 15;
                        }, 
                        []{ return "the user's age";}), 
                     makeInfoVariable([]{return 18;}, []{return "the allowed age";})
      );

Output:

lambda call#2
Requirement Helper Example#5: twenty {20} expected to be equal to twenty one 21

6. use bool nature and also log the success case

Requirements req6("Requirement Helper Example#6");
NDArray * arr= nullptr;
arr !=nullptr && req6.expectEq(arr->rankOf(), 3) ;
req6.logTheSuccess();

Output:

Requirement Helper Example#6: meets the requirements

7. custom comparision lambda and also another usage of the custom wrapper written by us ShapeInfoVariable. Note: we will use std::vector<int>. this wrapper can be used with NDArray as well.

Requirements req7("Requirement Helper Example#7");
req7.expect(makeShapeInfoVariable(std::vector<sd::LongType>{2,3,4,5}, SHAPE_MSG_INPUT0), makeShapeInfoVariable(std::vector<sd::LongType>{2,3,4,7}, SHAPE_MSG_INPUT1),
                    [](const std::vector<sd::LongType>& l, const std::vector<sd::LongType>& r){
                        return l == r;
                    }
                 , EXPECTED_EQ_MSG);
}

Output:

Requirement Helper Example#7: the Shape of the Input NDArray#0 {[2, 3, 4, 5]} expected to be equal to the Shape of the Input NDArray#1 [2, 3, 4, 7]

8. throw error when there is failure

Requirements req8("Requirement Helper Example#8");
req8.expectEq(6,6) &&
req8.expectIn(6, {1,2,3,7,8,9});
req8.throws();

Output:

terminate called after throwing an instance of 'std::invalid_argument'
  what():  Op validation failed
...
Requirement Helper Example#8: {6} expected to be one of these {[1, 2, 3, 7, 8, 9, ]}

Here is live example:

Note: some classes were mocked there and do not represent the exact implementations in libnd4j. https://godbolt.org/z/sq98vchs5