macos - What constant can I use for the default Aqua space in Autolayout?

Question

According to the Cocoa Auto Layout Guide, I can use a dash in the visual constraint format language to "denote the standard Aqua space:"

[self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"[a]-[b]"
                                                             options:0
                                                             metrics:nil
                                                               views:viewDict]];

However, I can't seem to find an NSLayout... constant or method that allows me to do the same thing if I'm building a constraint without using the visual format language:

[self addConstraint:[NSLayoutConstraint constraintWithItem:a
                                                 attribute:NSLayoutAttributeTrailing
                                                 relatedBy:NSLayoutRelationEqual
                                                    toItem:b
                                                 attribute:NSLayoutAttributeLeading
                                                multiplier:1.0f
                                                  constant:<# ??? #>]];

Is there a constant (or another value or method) that I can use to define the Aqua space in such a situation?

Answer 1

I've found the "standard Aqua space" to be 8.0 between sibling views, and 20.0 between a view and its superview.

NSView* view = [NSView new] ;
NSLayoutConstraint* constraintWithStandardConstantBetweenSiblings = [NSLayoutConstraint constraintsWithVisualFormat:@"[view]-[view]"  options:0  metrics:nil  views:NSDictionaryOfVariableBindings(view) ] [0] ;
CGFloat standardConstantBetweenSiblings = constraintWithStandardConstantBetweenSiblings.constant ;    // 8.0

NSView* superview = [NSView new] ;
[superview addSubview:view] ;
NSLayoutConstraint* constraintWithStandardConstantBetweenSuperview = [NSLayoutConstraint constraintsWithVisualFormat:@"[view]-|"  options:0  metrics:nil  views:NSDictionaryOfVariableBindings(view) ] [0] ;
CGFloat standardConstantBetweenSuperview = constraintWithStandardConstantBetweenSuperview.constant ;    // 20.0