Function Eval

go/engine/expr/expression.go:21–44

Eval evaluates an workflow.Expression against resolved references, returning a typed Value.

(expr workflow.Expression, resolve VarResolver)

// Eval evaluates an workflowapi.Expression against resolved references,
// returning a typed Value.
func Eval(expr workflowapi.Expression, resolve VarResolver) (Value, error) {
	plCount := len(placeholderRE.FindAllStringIndex(expr.Expression, -1))
	refCount := len(expr.References)
	if plCount != refCount {
		return Value{}, fmt.Errorf(
			"expression placeholders (%d) do not match references (%d)",
			plCount, refCount,
		)
	}

	refs := make([]Value, refCount)
	for i, ref := range expr.References {
		v, err := resolve.Resolve(ref)
		if err != nil {
			return Value{}, err
		}
		// An image has no text or scalar form; using one in an expression
		// would silently coerce the frame to an empty/zero value.
		if v.Type == workflowapi.Image {
			return Value{}, fmt.Errorf("an image value cannot be used in an expression")
		}
		refs[i] = v
	}

	if expr.DataType == workflowapi.String {
		return evalStringExpr(expr.Expression, refs)
	}