Inlining

When compiling a contract in LIGO, declarations will get inlined if they are only used once and pure. Inlining often results in larger contracts and is therefore not aggressively done.

A pure declaration is one that doesn't cause side effects like causing a failure or operation.

In some cases you might want to override the default behaviour of LIGO and force inlining. The declaration still needs to be pure though.

Inline attribute

To force inlining you can use the inline attribute.

function fst(const p : nat * nat) : nat is p.0; attributes ["inline"] ;
function main(const p : nat * nat; const s : nat * nat) : list(operation) * (nat * nat) is
((list end : list(operation)), (fst(p.0,p.1), fst(s.1,s.0)))

Now if we measure the difference between inlining and without inlining, using ligo measure-contract name_of_contract.ligo <entrypoint>, we see the following results:

With inlining66 bytes
Without inlining170 bytes
info

Note that these results can change due to ongoing work to optimize output of the LIGO compiler.