An ERB-style templating language for Go.
Ego is an ERb style templating language for Go. It works by transpiling templates into pure Go and including them at compile time. These templates are light wrappers around the Go language itself.
You can find a release build of ego for Linux on the Releases page.
To install ego from source, you can run this command outside of the
GOPATH:
$ go get github.com/benbjohnson/ego/...
Run
egoon a directory. Recursively traverse the directory structure and generate Go files for all matching
.egofiles.
$ ego mypkg
An ego template lets you write text that you want to print out but gives you some handy tags to let you inject actual Go code. This means you don't need to learn a new scripting language to write ego templates—you already know Go!
Any text the
egotool encounters that is not wrapped in
and%>tags is considered raw text. If you have a template like this:hello! goodbye!Then
egowill generate a matching.ego.gofile:io.WriteString(w, "hello!\ngoodbye!")Unfortunately that file won't run because we're missing a
packageline at the top. We can fix that with code blocks.Code Blocks
A code block is a section of your template wrapped in
and%>tags. It is raw Go code that will be inserted into our generate.ego.gofile as-is.For example, given this template:
hello! goodbye!The
egotool will generate:package myappimport ( "context" "io" )
func Render(ctx context.Context, w io.Writer) { io.WriteString(w, "hello!\ngoodbye!") }
Note the
contextandiopackages are automatically imported to your template. These are the only packages that do this. You'll need to import any other packages you use.Print Blocks
Our template is getting more useful. We now have actually runnable Go code. However, our templates typically need output text frequently so there are blocks specifically for this task called print blocks. These print blocks wrap a Go expression with
and%>tags.We can expand our previous example and add a type and fields to our code:
hello, ! goodbye, !
We now have a conditional around our
Greetfield and we are printing theNamefield. Our generated code will look like:package myappimport ( "context" "io" )
type NameRenderer struct { Name string Greet bool }
func Render(ctx context.Context, w io.Writer) { if r.Greet { io.WriteString(w, "hello, ") io.WriteString(w, html.EscapeString(fmt.Sprint(r.Name))) io.WriteString(w, "!") } else { io.WriteString(w, "goodbye, ") io.WriteString(w, html.EscapeString(fmt.Sprint(r.Name))) io.WriteString(w, "!") } }
Printing unescaped HTML
The
block will print your text as escaped HTML, however, sometimes you need the raw text such as when you're writing JSON. To do this, simply wrap your Go expression withand%>tags.Components
Simple code and print tags work well for simple templates but it can be difficult to make reusable functionality. You can use the component syntax to print types that implement this
Rendererinterface:type Renderer interface { Render(context.Context, io.Writer) }Component syntax look likes HTML. You specify the type you want to instantiate as the node name and then use attributes to assign values to fields. The body of your component will be assigned as a closure to a field called
Yieldon your component type.For example, let's say you want to make a reusable button that outputs Bootstrap 4.0 code: We can write this component as an ego template or in pure Go code. Here we'll write the component in Go:
package myappimport ( "context" "io" )
type Button struct { Style string Yield func() }
func (r *Button) Render(ctx context.Context, w io.Writer) { fmt.Fprintf(w,
<div class="btn btn-%s">
, r.Style) if r.Yield { r.Yield() } fmt.Fprintf(w,</div>
) }Now we can use that component from a template in the same package like this:
Don't click me!Our template automatically convert our component syntax into an instance and invocation of
Button:var EGO Button EGO.Style = "danger" EGO.Yield = func() { io.WriteString(w, "Don't click me!") } EGO.Render(ctx, w)Field values can be specified as any Go expression. For example, you could specify a function to return a value for
Button.Style:Don't click me!Named closures
The
Yieldis a special instance of a closure, however, you can also specify named closures using the::syntax.Given a component type:
type MyView struct { Header func() Yield func() }We can specify the separate closures like this:
<:header> This content will go in the Header closure.This content will go in the Yield closure.
Importing components from other packages
You can import components from other packages by using a namespace that matches the package name The
egonamespace is reserved to import types in the current package.For example, you can import components from a library such as bootstrap-ego:
Don't click me!Caveats
Unlike other runtime-based templating languages, ego does not support ad hoc templates. All templates must be generated before compile time.
Ego does not attempt to provide any security around the templates. Just like regular Go code, the security model is up to you.