struct_demo

Struct Marshaling Demo

This example demonstrates how to marshal and unmarshal Go structs to/from ClassAd format using struct tags.

Features Demonstrated

1. Simple Struct Marshaling - Convert basic Go structs to ClassAd format
2. Struct Tags - Use classad and json tags to control field names
3. Tag Options - omitempty and - for skipping fields
4. Nested Structs - Handle complex hierarchical data structures
5. Unmarshal - Parse ClassAd strings into Go structs
6. Round-trip - Verify marshal→unmarshal preserves data
7. Map Support - Work with map[string]interface{}

API Overview

Marshal

classadStr, err := classad.Marshal(v)

Converts a Go value to ClassAd format string. Works with:

• Structs
• Maps
• Slices/arrays
• Basic types (int, float, string, bool)

Unmarshal

err := classad.Unmarshal(classadStr, &v)

Parses a ClassAd string into a Go value. The target must be a pointer.

Struct Tags

classad Tag

Primary tag for controlling ClassAd marshaling:

type Job struct {
    ID   int    `classad:"JobId"`        // Use custom name
    Name string `classad:"Name,omitempty"` // Omit if zero value
    Temp string `classad:"-"`            // Skip this field
}

json Tag Fallback

If no classad tag is present, falls back to json tag:

type Config struct {
    Timeout int `json:"timeout"`  // Uses "timeout" in ClassAd
    Port    int                   // Uses "Port" (field name)
}

Tag Options

• Field name: classad:"custom_name"
• Skip field: classad:"-"
• Omit if empty: classad:"name,omitempty"

Examples

Basic Struct

type Job struct {
    ID   int
    Name string
}

job := Job{ID: 123, Name: "test"}
str, _ := classad.Marshal(job)
// [ID = 123; Name = "test"]

With Tags

type Job struct {
    JobID int    `classad:"ClusterId"`
    Owner string `classad:"Owner"`
}

job := Job{JobID: 100, Owner: "alice"}
str, _ := classad.Marshal(job)
// [ClusterId = 100; Owner = "alice"]

Nested Structs

type Config struct {
    Timeout int
}

type Job struct {
    ID     int
    Config Config
}

job := Job{ID: 123, Config: Config{Timeout: 30}}
str, _ := classad.Marshal(job)
// [ID = 123; Config = [Timeout = 30]]

Unmarshal

classadStr := `[JobId = 456; Owner = "bob"]`

type Job struct {
    JobID int    `classad:"JobId"`
    Owner string `classad:"Owner"`
}

var job Job
classad.Unmarshal(classadStr, &job)
// job.JobID = 456, job.Owner = "bob"

Running the Demo

go run main.go

Use Cases

This struct marshaling is useful for:

• Configuration files - Store configs in ClassAd format
• HTCondor integration - Work with HTCondor job descriptions
• Data serialization - Alternative to JSON for certain workflows
• Type-safe APIs - Use Go structs with ClassAd backend
• Testing - Easy conversion between Go types and ClassAds

Comparison with JSON

Notes

• Unexported fields are automatically skipped
• Zero values can be omitted with omitempty
• Unknown fields in ClassAd are ignored during unmarshal
• Type conversions are performed when possible (int ↔ float)