[RUNTIME] Add clear() function in tvm::Map class

[Beya2019]

std::map and std::unordered_map have the clear() member function to clear the contents.

tvm::Array also has the clear() member function.

In order to be consistent with tvm::Array/std::map/std::unordered_map, we add the clear() member function in tvm::Map class used existing function implementation

@tqchen @yzhliu Would you please have a look at this? Thanks very much.

[tqchen]

cc @junrushao1994

[junrushao]

@Beya2019 Thanks for the contribution! However, the change here may not be correct: never erase elements in the container when iterating them 🙂

[junrushao]

The best way to clear a tvm::Map might be just re-creating one IMO

[Beya2019]

The best way to clear a tvm::Map might be just re-creating one IMO

OK， according the suggestion, re-creating one call default constructor function: Map() { data_ = MapNode::Empty(); } , so clear function can call data_ = MapNode::Empty(); directly IMO

Do you think this is ok？

[junrushao]

That looks good. Would you like to add some unittests? Thanks a lot!

[Beya2019]

That looks good. Would you like to add some unittests? Thanks a lot!

OK. Add the unittests TEST(Map, Clear) in tests/cpp/container_test.cc. Please help review this submit again.Thanks a lot.

[junrushao]

LGTM. Thanks for the contribution!