Constructor of Border: Border.symmetric #45524

Use case

Currently, Border has 3 constructors:

• Border from 4 (top, right, bottom, left) BorderSide
• Border.fromBorderSide from single BorderSide that apply to all sides (top, right, bottom, left)
• Border.all factory that internally instantiate a BorderSide and call Border.fromBorderSide

I suggest a new factory constructor Border.symmetric.
A typical use case:

Container(
    padding: const EdgeInsets.symmetric(horizontal: 20.0, vertical: 2.0),
    decoration: const BoxDecoration(
      border: Border.symmetric(
        horizontal: BorderSide(width: 1.0, color: Color(0xFFFFDFDFDF)),
        vertical: BorderSide(width: 1.0, color: Color(0xFFFF7F7F7F)),
      ),
      color: Color(0xFFBFBFBF),
    ),
)

Although it is rare for borders that is not in the same width or same color. It is convenient for widgets having only either horizontal or vertical border, in which is rather more common.

Proposal

factory Border.symmetric({ BorderSide vertical = BorderSide.none, BorderSide horizontal = BorderSide.none })
or
const Border.symmetric({ BorderSide vertical = BorderSide.none, BorderSide horizontal = BorderSide.none })

Reason for having factory of this name:

TableBorder is a class similar to Border and it has these constructors.

• TableBorder from 6 BorderSide
• TableBorder factory that internally instantiate a BorderSide and call constructor
• TableBorder.symmetric factory which accepts two BorderSide for inside and outside

Reason for having parameters of name:

EdgeInsets also handles top, right, bottom, left sides, has EdgeInsets.symmetric that accepts horizontal and vertical as parameter.

I can work a PR.