# Go Templates
### Overview
1. **Purpose**: Templates in Go are used to dynamically generate text output, such as HTML, XML, or any structured text format. They are particularly useful in web applications for rendering HTML pages.
2. **Packages**:
- `text/template`: For generating text outputs.
- `html/template`: Specifically designed for HTML outputs, with added security features to prevent cross-site scripting (XSS) attacks.
### Example
```go
package main
import (
"os"
"text/template"
)
type User struct {
Name string
Age int
}
func main() {
// Define a template
tmpl := "Name: {{.Name}}, Age: {{.Age}}\n"
// Parse the template
t, err := template.New("user").Parse(tmpl)
if err != nil {
panic(err)
}
// Execute the template with data
user := User{"Alice", 30}
err = t.Execute(os.Stdout, user)
if err != nil {
panic(err)
}
}
```
### Application Domains
1. **Web Development**: Rendering HTML pages in web applications.
2. **Configuration Management**: Generating config files from templates.
3. **Code Generation**: Generating boilerplate code for various purposes.
### Go Projects Using Templates
1. **Hugo**: A popular static site generator that extensively uses Go templates for generating web pages.
Certainly, I'll replace the pseudocode section with details unique to Go templates and considerations when using them. I'll also add a section about `FuncMap`.
### Unique Aspects of Go Templates
1. **Context-Aware Escaping**: In `html/template`, context-aware escaping is applied. It automatically escapes values based on the context, making it safer for HTML generation.
2. **Pipeline Concept**: Go templates use the pipeline (`|`) concept to chain data through filters or functions.
3. **Actions**: Use of actions like `{{if .Condition}}`, `{{range .Collection}}`, which are more expressive compared to some other templating languages.
4. **Nested Template Definitions**: Go allows defining one template inside another using the `{{define "name"}}` action.
5. **No Safe Navigation Operator**: Unlike some templating languages, Go templates do not have a safe navigation operator, so nil values need to be carefully handled.
6. **Associative Array Limitations**: Unlike some languages, Go's templates handle maps with non-string keys in a limited manner.
### Considerations When Using Go Templates
1. **Data Passing**: Templates execute with a single dot (`.`) context, which can be any Go data structure. Planning how data is structured and accessed is crucial.
2. **Error Handling**: Errors can occur during parsing or execution of templates, requiring robust error handling mechanisms.
3. **Template Caching**: For efficiency, especially in web applications, parse templates once and execute them with different data.
4. **Concurrency**: The `html/template` package is safe for concurrent use, meaning multiple goroutines can execute the same template.
### FuncMap in Go Templates
A `FuncMap` is a map in Go that associates names with functions. In templates, `FuncMap` allows custom functions to be used within the template text. These functions can be applied to data, manipulate it, or provide custom logic within the template.
#### Example Usage of FuncMap
```go
package main
import (
"html/template"
"os"
"strings"
)
func main() {
// Define a FuncMap
funcs := template.FuncMap{"toUpperCase": strings.ToUpper}
// Define a template with a custom function
tmpl := `{{toUpperCase .Name}}`
// Create a template, attach the FuncMap, and parse the text
t, err := template.New("name").Funcs(funcs).Parse(tmpl)
if err != nil {
panic(err)
}
// Execute the template
err = t.Execute(os.Stdout, map[string]string{"Name": "Alice"})
if err != nil {
panic(err)
}
}
```
In this example, the function `toUpperCase` from `strings` package is made available in the template via `FuncMap`. It's then used to transform the input text.
### Citations
- For detailed technicalities on templates: [Go Docs: text/template](https://pkg.go.dev/text/template)
- Practical usage in web development: [Go Web Programming by Sau Sheong Chang](https://www.manning.com/books/go-web-programming)
- "The Go Programming Language" by Alan A. A. Donovan and Brian W. Kernighan: Chapter on templates for detailed understanding.
## Links
- [GitHub - valyala/quicktemplate: Fast, powerful, yet easy to use template engine for Go. Optimized for speed, zero memory allocations in hot paths. Up to 20x faster than html/template](https://github.com/valyala/quicktemplate)