# Coding Tips and Style¶

## Coding Tips¶

Adding New Operations: One of the most common things that one will want to do to modify DyNet is to add a new operation to calculate a new function. You can find more information on how to do so at the end of the tutorial slides here.

## Coding Practices¶

Testing: Before committing any code, tests should be run to make sure that the new code didn’t break anything. This can be done by using the make test command. It is also highly recommended that you add unit tests for any new functionality. Unit tests are implemented in the tests directory. When making a bug fix, you can add a test that broke before the fix but passes afterwards.

That being said, tests are not an absolute requirement, so if you have a contribution but aren’t sure how to do tests, please don’t let this stop you from contributing.

## Coding Style Conventions¶

DyNet (the main version in C++) has certain coding style standards:

Overall Philosophy: DyNet is designed to minimize the computational overhead when creating networks. Try to avoid doing slow things like creating objects or copying memory in places that will be called frequently during computation graph construction.

Function Names: Function names are written in “snake_case”.

const: Always use const if the input to a function is constant.

Pointer vs. Reference: When writing functions, use the following guidelines (quoted from here):

• Only pass a value by pointer if the value 0/NULL is a valid input in the current context.
• If a function argument is an out-value, then pass it by reference.
• Choose “pass by value” over “pass by const reference” only if the value is a POD (Plain Old Datastructure) or small enough (memory-wise) or in other ways cheap enough (time-wise) to copy.

Error handling: The C++ core of DyNet provides a mechanism for error handling that should be used in all code. It consists of 3 macros as follows (included in globals.h):

• DYNET_INVALID_ARG(msg): This is used to throw an error that is triggered when a user passes an invalid argument to one of the functions.
• DYNET_RUNTIME_ERR(msg): This is used to throw an error that could be triggered by a user, but is not the result of an invalid argument. For example, it could be used when something is not implemented yet, or when the program dies due to lack of memory, etc.
• DYNET_ASSERT(expr,msg): This is to be used to check things that should only happen due to a programming error within DyNet itself, and should never be triggered by a user. expr is a condition, and msg is a message explaining the exception, with ostream-style formatting.