Trait handlebars::HelperDef [−] [src]

pub trait HelperDef: Send + Sync {
    fn call(&self,
            h: &Helper,
            r: &Registry,
            rc: &mut RenderContext)
            -> Result<(), RenderError>;
}

Helper Definition

Implement HelperDef to create custom helper. You can retrieve useful information from these arguments.

  • &Helper: current helper template information, contains name, params, hashes and nested template
  • &Registry: the global registry, you can find templates by name from registry
  • &mut RenderContext: you can access data or modify variables (starts with @)/patials in render context, for example, @index of #each. See its document for detail.

By default, you can use bare function as helper definition because we have supported unboxed_closure. If you have stateful or configurable helper, you can create a struct to implement HelperDef.

Define an inline helper

use handlebars::*;

fn upper(h: &Helper, _: &Handlebars, rc: &mut RenderContext) -> Result<(), RenderError> {
   // get parameter from helper or throw an error
   let param = h.param(0).and_then(|v| v.value().as_string()).unwrap_or("");
   try!(rc.writer.write(param.to_uppercase().into_bytes().as_ref()));
   Ok(())
}

Define block helper

Block helper is like #if or #each which has a inner template and an optional inverse template (the template in else branch). You can access the inner template by helper.template() and helper.inverse(). In most case you will just call render on it.

use handlebars::*;

fn dummy_block(h: &Helper, r: &Handlebars, rc: &mut RenderContext) -> Result<(), RenderError> {
    h.template().map(|t| t.render(r, rc)).unwrap_or(Ok(()))
}

Required Methods

Implementors