Method narrowTypeByTypeFacts

internal/checker/flow.go:673–688

(t *Type, impliedType *Type, facts TypeFacts)

}

func (c *Checker) narrowTypeByTypeFacts(t *Type, impliedType *Type, facts TypeFacts) *Type {
	return c.mapType(t, func(t *Type) *Type {
		switch {
		case c.isTypeRelatedTo(t, impliedType, c.strictSubtypeRelation):
			if c.hasTypeFacts(t, facts) {
				return t
			}
			return c.neverType
		case c.isTypeSubtypeOf(impliedType, t):
			return impliedType
		case c.hasTypeFacts(t, facts):
			return c.getIntersectionType([]*Type{t, impliedType})
		}
		return c.neverType
	})
}

func (c *Checker) narrowTypeByDiscriminantProperty(t *Type, access *ast.Node, operator ast.Kind, value *ast.Node, assumeTrue bool) *Type {
	if (operator == ast.KindEqualsEqualsEqualsToken || operator == ast.KindExclamationEqualsEqualsToken) && t.flags&TypeFlagsUnion != 0 {