https://github.com/SnapKit/SnapKit
box.snp_makeConstraints { (make) -> Void in
make.width.height.equalTo(50)
make.center.equalTo(self.view)
}https://github.com/SnapKit/Masonry
[box mas_makeConstraints:^(MASConstraintMaker* make) {
make.width.height.equalTo(50);
make.center.equalTo(self.view);
}];https://github.com/robb/Cartography
constrain(button1, button2) { button1, button2 in
button1.right == button2.left - 12
} [box.widthAnchor constraintEqualToConstant:50].active = YES;
[box.centerAnchor constrantEqualToAnchor:self.view.centerAnchor].active = YES;https://github.com/viewfinderco/viewfinder/blob/master/clien...
[self addConstraints:box.anchorWidth == 50];
[self addConstraints:box.anchorHeight == 50];
[self addConstraints:box.anchorCenterX == self.view.anchorCenterX];
[self addConstraints:box.anchorCenterY == self.view.anchorCenterY];