Text Placeholder
Text Placeholder is a minimalistic text template engine designed for the manipulation of named placeholders within textual templates.
This library operates based on two primary elements:
-
Placeholders: Defined markers within the text templates intended to be replaced by actual content in the final rendition.
-
Context: The precise data set used for the replacement of placeholders during the template rendering process.
For use within a no_std
environment, Text
Placeholder can be configured by disabling
the default features.
This allows the library to maintain compatibility with no_std
specifications.
Placeholders
Placeholders are defined within certain boundaries and will be replaced once the template is parsed.
Let's define a template with placeholders named first
and second
:
let template = new;
Templates use the handlebars syntax as boundaries by default, but can be overridden:
let template = new_with_placeholder;
Context
Context is the data structure that will be used to replace your placeholders with real data.
You can think of your placeholder as a key within a HashMap
or the name of a field within a
struct
. In fact, these are the three types of context supported by this library:
- HashMap.
- A function
- Struct, as an optional feature.
HashMap
Each placeholder should be a key
with an associated value
that can be converted into a str
.
The following methods are available with a HashMap
:
fill_with_hashmap
- replaces missing placeholders with an empty string.
- replaces placeholders that cannot be converted to a strint with an empty string.
fill_with_hashmap_strict
which returns aError::PlaceholderError
when:- a placeholder is missing.
- a placeholder value cannot be converted to a string.
Example
use Template;
use HashMap; // or for no_std `use hashbrown::HashMap;`
let default_template = new;
let mut table = new;
table.insert;
table.insert;
assert_eq!;
// We can also specify our own boundaries:
let custom_template = new_with_placeholder;
assert_eq!;
Function
This uses a function to generate the substitution value. The value could be extracted from a HashMap or BTreeMap, read from a config file or database, or purely computed from the key itself.
The function takes a key
and returns an Option<Cow<str>>
- that is it can return a borrowed
&str
, an owned String
or no value. Returning no value causes fill_with_function
to fail (it's
the equivalent of fill_with_hashmap_strict
in this way).
The function actually a FnMut
closure, so it can also modify external state, such as keeping track
of which key
values were used. key
has a lifetime borrowed from the template, so it can be
stored outside of the closure.
Example
use Template;
use Cow;
let template = new;
let mut idx = 0;
assert_eq!;
assert_eq!;
Struct
Allow structs that implement the serde::Serialize
trait to be used as context.
This is an optional feature that depends on serde
. In order to enable it add the following to your
Cargo.toml
file:
[]
= { = "0.4", = ["struct_context"] }
Each placeholder should be a field
in your struct
with an associated value
that can be
converted into a str
.
The following methods are available with a struct
:
fill_with_struct
- replaces missing placeholders with an empty string.
- replaces placeholders that cannot be converted to a strint with an empty string.
fill_with_struct_strict
which returns aError::PlaceholderError
when:- a placeholder is missing.
- a placeholder value cannot be converted to a string.
Example
use Template;
let default_template = new;
let context = Context ;
assert_eq!;
// We can also specify our own boundaries:
let custom_template = new_with_placeholder;
assert_eq!;