iOS Swift. Difference between leftAnchor and leadingAnchor

When we working with constraint programatically we can have two options for left side: leadingAnchor and leftAnchor, the same for right side: rightAnchor and trailingAnchor.

What is the difference between this anchors?

for left side

self.view.leftAnchor

and

self.view.leadingAnchor

for right side:

self.view.rightAnchor

and

self.view.trailingAnchor

leftAnchor and rightAnchor are strongly fixed and always depend on the left and right sides of the screen. leadingAnchor and trailingAnchor are flexible and depend on the device locale. For locales, where the spelling is from left to right this anchors can be used interchangeably(left with leading and right with trailing). For locales, where the spelling is from right to left leadingAnchor will depend on the right side and trailingAnchor will depend the left side.

For example, you have a screen on which the label is located on the left and textfield on the right for the locale where the writing is from left to right. For a locale where the spelling is from right to left label will be located right and textfield on the left.

You should always use leadingAnchor and trailingAnchor instead of leftAnchor and rightAnchor unless you have special requirements that say that the interface elements are always depend on the left or on the right.

If you want the interface element to be on the screen on the left or right depending on the locale, then use leadingAnchor and trailingAnchor, respectively.

If you want the interface element to always be located on the left or right, regardless of the locale, then use leftAnchor and rightAnchor , respectively.