Code style guide

MOM6 code style guide

Code style is typically a personal choice. When styles clash

White space

• No tabs
• No trailing white space
• Indents should be consistent (some amount used in contiguous blocks)
• Preferred indent is 2 spaces
• No white space between a function name and the parenthesis
• White space after all language token
  • if(a==0) is legal fortran but bad style. Use if (a==0) instead.

Local variables

• Local variable declarations appear after all the dummy argument declarations. We typically use ! Local variables to delineate between the argument and local variable declarations.
• Local variables should preferably be descriptive multi-character names meaningful in their context, e.g. del_rho_int (delta rho at interface). If using a highly abbreviated or short name, the declaration MUST be commented.

Loop indices

Soft case convention

• i,j,k are used for cell-center, layer-center references, e.g. h(i,j,k), T(i+1,j,k).
• I,J are used for staggered, cell-edge references, e.g. u(I,j,k), v(i,J,k), q(I,J,k), u(I-1,j,k). We use a north-east staggering convention so the I means i+1/2 and I-1 means i-1/2.
• K is used for the interface (between layer) references, e.g. del_t(i,j,K) = T(i,j,K+1) - T(i,j,K). The vertical staggering is such that interface K=1 is above layer k=1 so that K means k-1/2 and K+1 means k+1/2.

Global / module data

• Absolutely NO!
• There are a few exceptions which are strictly for debugging non-shared memory applications. Do not use these as an excuse for added module data.

Data flow

• All needed data is passed via arguments to subroutines and functions, or as the returned value of a function.
• All arguments must have declared intent, with the exception of pointers: i.e. intent(in), intent(out), intent(inout).
• Opaque types are preferred, i.e. referencing members of types defined in other modules is discouraged.