← Library Predicate Deterministic

IfStringHasPrefixOp

Returns true if string A starts with string B.

Inputs

FieldTypeDescription
A*stringString to test
B*stringExpected prefix

Outputs

FieldTypeDescription
MatchboolTrue when A starts with B

Typical Use Cases

  • Namespace or path prefix detection
  • Command prefix routing
  • Protocol or scheme checking

Complete Runnable Example

Checks whether a user message starts with "/" to detect a slash command versus free-form input.

main.go
package main

import (
	"context"
	"encoding/json"
	"log"
	"os"
	"time"

	"github.com/akennis/sparsi-go/library"
	_ "github.com/akennis/dagor/operator/builtin"

	"github.com/panjf2000/ants/v2"
	"github.com/akennis/dagor"
	"github.com/akennis/dagor/graph"
)

func main() {
	text, prefix := "/help me with billing", "/"
	library.RegisterConst("text_val", text)
	library.RegisterConst("prefix_val", prefix)

	g, err := graph.NewBuilder("hasprefix_demo").
		Vertex("src_a").Op("text_val").Output("Result", "wire_a").
		Vertex("src_b").Op("prefix_val").Output("Result", "wire_b").
		Vertex("check").Op("IfStringHasPrefixOp").
		Input("A", "wire_a").Input("B", "wire_b").
		Output("Match", "is_command").
		Build()
	if err != nil {
		log.Fatalf("build: %v", err)
	}

	pool, err := ants.NewPool(4)
	if err != nil {
		log.Fatalf("pool: %v", err)
	}
	defer pool.Release()

	eng, err := dagor.NewEngine(g, pool)
	if err != nil {
		log.Fatalf("engine: %v", err)
	}

	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
	defer cancel()

	if err := eng.Run(ctx); err != nil {
		log.Fatalf("run: %v", err)
	}

	out := map[string]any{"text": text, "prefix": prefix}
	if raw, ok := eng.GetOutput("is_command"); ok {
		out["is_command"] = *raw.(*bool)
	}
	enc := json.NewEncoder(os.Stdout)
	enc.SetIndent("", "  ")
	enc.Encode(out)
}