Crate declarative_env 

This crate contains a macro for generating a struct which reads the environmental variables defined in the configured file.

This allows to have a single point of definition for the env configuration, thus avoiding a possible incoherence between the documentation and the implementation.

Usage

The macro must be attached to an empty struct definition:

   #[declarative_env(path = "./example.hjson", format = "hjson")]
   struct MyConfig;

Note: the struct can have any visibility.

The macro creates a struct with the same name of the empty struct, but it injects as fields all the variables defined in the path keyword.

For example, the definition file:

SERVER_PORT: {
   type: u16
   description: The port the server will listen on
   default: 8080
}

generates the struct

struct MyConfig {
   SERVER_PORT: u16,
}

The path of the definition file is relative to the cargo manifest dir (the one with Cargo.toml).

The supported formats are specified in the AcceptedFormat enum; formats are the lowercase version of the enum variants, so AcceptedFormat::Hjson is selected with format = "hjson".

Env Variable Definition

The env variable definition file contains a map of objects, where the key is the name of the env variable, and the value contains the metadata of the variable:

• the type (accepted types are defined in AcceptedRustType).
• the description, unused in generated code, required for documentation purpose.
• the default value, optional (it must be parsable as the defiend type).

Accepted formats

This crate supports the following formats for the definition file:

• hjson

Accepted types

This crate supports the following types for the variables defined:

• iX (X = {8, 16, 32, 64, 128})
• uX (X = {8, 16, 32, 64, 128})
• bool
• String
• f32,f64

Attribute Macros

declarative_env

This is the entrypoint for the crate.