noinline

final

An annotation for methods that the optimizer should not inline.

Note that by default, the Scala optimizer is disabled and no callsites are inlined. See -opt:help for information how to enable the optimizer and inliner.

When inlining is enabled, the inliner will never inline methods or callsites annotated @noinline.

Examples:

@inline   final def f1(x: Int) = x
@noinline final def f2(x: Int) = x
         final def f3(x: Int) = x

def t1 = f1(1)              // inlined if possible
def t2 = f2(1)              // not inlined
def t3 = f3(1)              // may be inlined (the inliner heuristics can select the callsite)
def t4 = f1(1): @noinline   // not inlined (override at callsite)
def t5 = f2(1): @inline     // inlined if possible (override at callsite)
def t6 = f3(1): @inline     // inlined if possible
def t7 = f3(1): @noinline   // not inlined
}

Note: parentheses are required when annotating a callsite within a larger expression.

def t1 = f1(1) + f1(1): @noinline   // equivalent to (f1(1) + f1(1)): @noinline
def t2 = f1(1) + (f1(1): @noinline) // the second call to f1 is not inlined
Source
noinline.scala
class Object
trait Matchable
class Any