EdgeInsetsDirectional.only constructor

const EdgeInsetsDirectional.only({double start: 0.0, double top: 0.0, double end: 0.0, double bottom: 0.0 })

Creates insets with only the given values non-zero.

A margin indent of 40 pixels on the leading side: 
const EdgeInsetsDirectional.only(start: 40.0)

Implementation 

const EdgeInsetsDirectional.only({
  this.start = 0.0,
  this.top = 0.0,
  this.end = 0.0,
  this.bottom = 0.0
});