Eric Niebler wrote:
1) a reduction in interface complexity. - one lock class, instead of a scoped_lock, try_lock, timed_lock, etc. - no bools or enums in constructors; instead, there are clearly named factory functions for customizing lock construction.
2) You can initialize a lock in the condition of an "if" statement.
3) You can return a lock from a function. (Benefit is debatable.)
After giving it some thought: - one lock class: tie; - no bools or enums in constructors: there is a bool argument, but it's (in my opinion) acceptable since there is a single constructor, and the argument participates directly in its postcondition: Lock( Mutex & m, bool l = true ); Post: locked() == l; - you can return a lock from a function: we can make the locks movable regardless of the interface, so it seems possible to ignore this bullet; - if( lock l = try_lock( m ) ) { } This is the main difference. Declarations in conditions are a nice idiom. The typical use is if( X x = f() ) { // do something with x } Our example doesn't fit the pattern, however, as the "// do something" part typically does not reference the lock itself. I don't have much experience with try locks, though. Pretty much the only example that comes to mind is Howard's lock_both: for(;;) { l1.lock(); if( l2.try_lock() ) return; l1.unlock(); l2.lock(); if( l1.try_lock() ) return; l2.unlock(); } (I hope I got that right) and I don't see how it can be improved by the if() idiom. But I may be missing some important use cases.