@sdyalor can you provide a image/ visual representation of want you want please ?

@sdyalor your example forces the entire width because you are using pipes on both sides which creates a constraint with default margins to the edges. With |-a-10-b-| view a is given a left constraint to it's container's left + default margin. view b is given a left constraint to be view a's right + 10 AND a right constraint to be it's container's right - default margin. If you removed the pipes and just did a-10-b then they will not span the whole width. They would likely be left aligned because autolayout has no other instructions of how to lay them out.
if you wanted them centered with 10 pixels between them it's easier to to use the dot notation and do:

a.Right == parent.Center - 5
b.Left == parent.Center + 5

where parent might be an implied "self" depending on the complexity of your layout.