clap allows you to provide list of accepted values using possible_values like this.
let mode_vals = ["fast", "slow"];
.possible_values(&mode_vals)
How to do this with structopt?
Since structopt 0.3, you can use any method from App and Arg directly:
const MODE_VALS: &[&str] = &["fast", "slow"];
#[derive(StructOpt, Debug)]
struct Opt {
/// The velocity mode
#[structopt(short, long, possible_values(MODE_VALS))]
mode: String,
}
https://github.com/TeXitoi/structopt/blob/master/CHANGELOG.md#raw-attributes-are-removed-198-by-sphynx
clap’s possible_values is exposed as a field option, as shown in this structopt example:
//! How to use `arg_enum!` with `StructOpt`.
use clap::arg_enum;
use structopt::StructOpt;
arg_enum! {
#[derive(Debug)]
enum Baz {
Foo,
Bar,
FooBar
}
}
#[derive(StructOpt, Debug)]
struct Opt {
/// Important argument.
#[structopt(possible_values = &Baz::variants(), case_insensitive = true)]
i: Baz,
}
fn main() {
let opt = Opt::from_args();
println!("{:?}", opt);
}
Notably, this is making use of case_insensitive as well, to allow any case of those variants to be accepted.
If you want more granular control, you could omit case_insensitive and instead implement the variants yourself:
use structopt::StructOpt;
#[derive(Debug)]
enum Baz {
Foo,
Bar,
FooBar
}
impl Baz {
fn variants() -> [&'static str; 3] {
["foo", "bar", "foo-bar"]
}
}
#[derive(StructOpt, Debug)]
struct Opt {
/// Important argument.
#[structopt(possible_values = &Baz::variants())]
i: Baz,
}
fn main() {
let opt = Opt::from_args();
println!("{:?}", opt);
}
Finally, you could also use a string array in the same manner.
Related
I have a data model that I would like to be deserialized from "camelCase" to the rust standard "snake_case" when reading from a source, X. But I'd like to leave it in "snake_case" when reading or writing to another source, Y.
For example, the following code,
#[derive(Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
struct Data {
foo_bar: String,
hello_word: String,
}
can only be encoded and decoded in camel case. Even if I manually defined my Serialize and Deserialize implementations, I can't define multiple for the same struct. I could define a second struct that's a copy/paste of the other and then derive but that method would get tedious with multiple large structs. What I would really like to do is specify that rename_all attribute at run-time. But I'm not seeing any way to do that in serde's API.
I think the best way sigh is to just write out one struct Data_ per #[serde(rename_all = ...)], then write one additional struct Data that will be the in-memory representation (which won't be serializable, to remove ambiguity), then implement From in both directions for the Data_s and Data so that they're interconvertible.
Thankfully, we can use a macro so that we only have to specify the fields once. (It is incredibly disgusting nonetheless.)
This playground available here.
use serde::{Deserialize, Serialize}; // 1.0.130
use serde_json; // 1.0.69
macro_rules! interconvertible {
($T:ident <-> $U:ident, $($field_name:ident),*) => {
impl From<$T> for $U {
fn from(t: $T) -> Self {
let $T { $($field_name),* } = t;
Self { $($field_name),* }
}
}
impl From<$U> for $T {
fn from(u: $U) -> Self {
let $U { $($field_name),* } = u;
Self { $($field_name),* }
}
}
};
}
macro_rules! create_data_structs {
($($field_name:ident: $field_type:ty),* $(,)?) => {
#[derive(Serialize, Deserialize, Debug)]
#[serde(rename_all = "camelCase")]
struct DataX {
$($field_name: $field_type),*
}
#[derive(Serialize, Deserialize, Debug)]
#[serde(rename_all = "snake_case")]
struct DataY {
$($field_name: $field_type),*
}
#[derive(Debug)]
struct Data {
$($field_name: $field_type),*
}
interconvertible!(DataX <-> Data, $($field_name),*);
interconvertible!(DataY <-> Data, $($field_name),*);
}
}
create_data_structs!(foo_bar: String, hello_world: String);
fn main() -> serde_json::Result<()> {
let x1: DataX = serde_json::from_str(r#"{"fooBar": "a", "helloWorld": "b"}"#)?;
let y1: DataY = serde_json::from_str(r#"{"foo_bar": "a", "hello_world": "b"}"#)?;
println!("{:?}, {:?}", x1, y1);
let x2: Data = x1.into();
let y2: Data = y1.into();
println!("{:?}, {:?}", x2, y2);
let x_string = serde_json::to_string(&DataX::from(x2))?;
let y_string = serde_json::to_string(&DataY::from(y2))?;
println!("{:?}, {:?}", x_string, y_string);
Ok(())
}
The output is:
DataX { foo_bar: "a", hello_world: "b" }, DataY { foo_bar: "a", hello_world: "b" }
[Data { foo_bar: "a", hello_world: "b" }, Data { foo_bar: "a", hello_world: "b" }]
"{\"fooBar\":\"a\",\"helloWorld\":\"b\"}", "{\"foo_bar\":\"a\",\"hello_world\":\"b\"}"
Since I'm only every decoding from source X I can utilize the #[serde(alias = ???)] macro. So my above use case would be
#[derive(Serialize, Deserialize)]
struct Data {
#[serde(alias="fooBar")]
foo_bar: String,
#[serde(alias="helloWorld")]
hello_word: String,
}
It's still a little tedious but better than an intermediate struct. It won't work though if I want to decode or encode to different cases.
(I'm not going to mark this as an answer because it's a work-around for my specific use case. If anyone has a more generic solution feel free to answer.)
I'm using the enum_dispatch crate and want to wrap some of my MyBehaviorEnums in a Mutex, then insert them into a HashMap. Without the Mutex, when I get items from the HashMap, I can easily pattern match for different MyBehaviorEnum values. But I'm not exactly sure how to do this kind of matching when the MyHeaviorEnum values are wrapped in a Mutex, or what an idiomatic approach might look like.
enum_dispatch = "0.3.7"
use core::convert::TryInto;
use enum_dispatch::enum_dispatch;
use std::sync::Mutex;
use std::collections::HashMap;
struct MyImplementorA {}
impl MyBehavior for MyImplementorA {
fn my_trait_method(&self) {}
}
struct MyImplementorB {}
impl MyBehavior for MyImplementorB {
fn my_trait_method(&self) {}
}
#[enum_dispatch]
enum MyBehaviorEnum {
MyImplementorA,
MyImplementorB,
}
#[enum_dispatch(MyBehaviorEnum)]
trait MyBehavior {
fn my_trait_method(&self);
}
fn main() {
//No Mutex wrapper
let a: MyBehaviorEnum = MyImplementorA {}.into();
let a2: MyBehaviorEnum = MyImplementorA {}.into();
let mut map = HashMap::new();
map.insert("First", a);
map.insert("Second", a2);
match map.get_mut("First"){
Some(MyBehaviorEnum::MyImplementorA(a_instance)) =>{
a_instance.my_trait_method();
}
_=>()
}
//Implementor enum values are wrapped in Mutex then inserted into HashMap
let a: MyBehaviorEnum = MyImplementorA {}.into();
let a2: MyBehaviorEnum = MyImplementorA {}.into();
let mut map = HashMap::new();
map.insert("First", Mutex::new(a));
map.insert("Second", Mutex::new(a2));
match map.get_mut("First"){
Some(mutex_impl_a)=>{
match Mutex::into_inner(mutex_impl_a){
Ok(MyBehaviorEnum::MyImplementorA(a_instance)) =>{
a_instance.my_trait_method();
}
_=>()
}
}
}
}
When working with the mutex wrapped values, use:
match map.get_mut("First"){
Some(mutex_impl_a)=>{
match &*mutex_impl_a.lock().unwrap(){
MyBehaviorEnum::MyImplementorA(a_instance)=>{
dbg!("got it!");
}
_=>()
}
}
_=>()
}
I want to iterate over over the fields of a struct and access its respective value for each iteration:
#[derive(Default, Debug)]
struct A {
foo: String,
bar: String,
baz: String
}
fn main() {
let fields = vec!["foo", "bar", "baz"];
let a: A = Default::default();
for field in fields {
let value = a[field] // this doesn't work
}
}
How can I access a field by variable?
Rust doesn't have any way of iterating directly over its fields. You should instead use a collection type such as Vec, array or one of the collections in std::collections if your data semantically represents a collection of some sort.
If you still feel the need to iterate over the fields, perhaps you need to re-consider your approach to your task and see if there isn't a more idiomatic/proper way to accomplish it
By using pattern matching, you can iterate over its fields.
#[derive(Default, Debug)]
struct A {
foo: String,
bar: String,
baz: String
}
impl A {
fn get(&self, field_string: &str) -> Result<&String, String> {
match field_string {
"foo" => Ok(&self.foo),
"bar" => Ok(&self.bar),
"baz" => Ok(&self.baz),
_ => Err(format!("invalid field name to get '{}'", field_string))
}
}
}
fn main() {
let fields = vec!["foo", "bar", "baz"];
let a = A {
foo: "value_of_foo".to_string(),
bar: "value_of_bar".to_string(),
baz: "value_of_baz".to_string()
};
for field in fields {
let value = a.get(field).unwrap();
println!("{:?}", value);
}
}
returns
"value_of_foo"
"value_of_bar"
"value_of_baz"
I am now writing a macro that implements such codes automatically for any struct, although there may be some bugs.
field_accessor (https://github.com/europeanplaice/field_accessor).
Cargo.toml
[dependencies]
field_accessor = "0"
use field_accessor::FieldAccessor;
#[derive(Default, Debug, FieldAccessor)]
struct A {
foo: String,
bar: String,
baz: String
}
fn main() {
let a = A {
foo: "value_of_foo".to_string(),
bar: "value_of_bar".to_string(),
baz: "value_of_baz".to_string()
};
for field in a.getstructinfo().field_names.iter() {
let value = a.get(field).unwrap();
println!("{:?}", value);
}
}
It also returns
"value_of_foo"
"value_of_bar"
"value_of_baz"
Based on the answer of sshashank124 I came to the conclusion that I should use an Hashmap instead of a struct:
fn main() {
let mut B = HashMap::new();
B.insert("foo", 1);
B.insert("bar", 2);
B.insert("baz", 3);
let fields = vec!["foo", "bar", "baz"];
for &field in &fields {
let value = B.get(field);
}
}
I can do this:
enum MyEnum {
A(i32),
B(i32),
}
but not this:
enum MyEnum {
A(123), // 123 is a constant
B(456), // 456 is a constant
}
I can create the structures for A and B with a single field and then implement that field, but I think there might be an easier way. Is there any?
The best way to answer this is working out why you want constants in an enum: are you associating a value with each variant, or do you want each variant to be that value (like an enum in C or C++)?
For the first case, it probably makes more sense to just leave the enum variants with no data, and make a function:
enum MyEnum {
A,
B,
}
impl MyEnum {
fn value(&self) -> i32 {
match *self {
MyEnum::A => 123,
MyEnum::B => 456,
}
}
}
// call like some_myenum_value.value()
This approach can be applied many times, to associate many separate pieces of information with each variant, e.g. maybe you want a .name() -> &'static str method too. In the future, these functions can even be marked as const functions.
For the second case, you can assign explicit integer tag values, just like C/C++:
enum MyEnum {
A = 123,
B = 456,
}
This can be matched on in all the same ways, but can also be cast to an integer MyEnum::A as i32. (Note that computations like MyEnum::A | MyEnum::B are not automatically legal in Rust: enums have specific values, they're not bit-flags.)
Creating an "enum" with constant values, can be augmented using structs and associated constants.
This is similar to how crates like bitflags works and what it would generate.
Additionally, to prevent direct instantiation of MyEnum you can tag it with #[non_exhaustive].
#[non_exhaustive]
struct MyEnum;
impl MyEnum {
pub const A: i32 = 123;
pub const B: i32 = 456;
}
Then you simply use the "enum" as you otherwise would, by accessing MyEnum::A and MyEnum::B.
People looking at this may stumble upon the introduction and deprecation of FromPrimitive. A possible replacement which might also be useful here is enum_primitive. It allows you to use C-like enums and have them cast between numeric and logical representation:
#[macro_use]
extern crate enum_primitive;
extern crate num;
use num::FromPrimitive;
enum_from_primitive! {
#[derive(Debug, PartialEq)]
enum FooBar {
Foo = 17,
Bar = 42,
Baz,
}
}
fn main() {
assert_eq!(FooBar::from_i32(17), Some(FooBar::Foo));
assert_eq!(FooBar::from_i32(42), Some(FooBar::Bar));
assert_eq!(FooBar::from_i32(43), Some(FooBar::Baz));
assert_eq!(FooBar::from_i32(91), None);
}
The enum-map crate provides the ability to assign a value to the enum record. What is more, you can use this macro with different value types.
use enum_map::{enum_map, Enum}; // 0.6.2
#[derive(Debug, Enum)]
enum Example {
A,
B,
C,
}
fn main() {
let mut map = enum_map! {
Example::A => 1,
Example::B => 2,
Example::C => 3,
};
map[Example::C] = 4;
assert_eq!(map[Example::A], 1);
for (key, &value) in &map {
println!("{:?} has {} as value.", key, value);
}
}
How about this?
enum MyEnum {
A = 123,
B = 456,
}
assert_eq!(MyEnum::A as i32, 123i32);
assert_eq!(MyEnum::B as i32, 456i32);
Just to give another idea.
#[allow(non_snake_case, non_upper_case_globals)]
mod MyEnum {
pub const A: i32 = 123;
pub const B: i32 = 456;
}
Then you can simply use it by accessing MyEnum::A and MyEnum::B or use MyEnum::*.
The advantage of doing this over associated constants is that you can even nest more enums.
#[allow(non_snake_case, non_upper_case_globals)]
mod MyEnum {
pub const A: i32 = 123;
pub const B: i32 = 456;
#[allow(non_snake_case, non_upper_case_globals)]
mod SubEnum {
pub const C: i32 = 789;
}
}
For my project I wrote a macro that automatically generates indexes and sets initial values.
#[macro_export]
macro_rules! cnum {
(#step $_idx:expr,) => {};
(#step $idx:expr, $head:ident, $($tail:ident,)*) => {
pub const $head: usize = $idx;
cnum!(#step $idx + 1usize, $($tail,)*);
};
($name:ident; $($n:ident),* $(,)* $({ $($i:item)* })?) => {
cnum!($name; 0usize; $($n),* $({ $($i)* })?);
};
($name:ident; $start:expr; $($n:ident),* $(,)* $({ $($i:item)* })?) => {
#[macro_use]
#[allow(dead_code, non_snake_case, non_upper_case_globals)]
pub mod $name {
use crate::cnum;
$($($i)*)?
cnum!(#step $start, $($n,)*);
}
};
}
Then you can use it like this,
cnum! { Tokens;
EOF,
WhiteSpace,
Identifier,
{
cnum! { Literal; 100;
Numeric,
String,
True,
False,
Nil,
}
cnum! { Keyword; 200;
For,
If,
Return,
}
}
}
I have created a crate enumeration just for this.
Example using my crate:
use enumeration::prelude::*;
enumerate!(MyEnum(u8; i32)
A = 123
B = 456
);
pub fn main() {
assert_eq!(*MyEnum::A.value(), 123);
assert_eq!(*MyEnum::B.value(), 456);
}
Say we want to have objects implementations switched at runtime, we'd do something like this:
pub trait Methods {
fn func(&self);
}
pub struct Methods_0;
impl Methods for Methods_0 {
fn func(&self) {
println!("foo");
}
}
pub struct Methods_1;
impl Methods for Methods_1 {
fn func(&self) {
println!("bar");
}
}
pub struct Object<'a> { //'
methods: &'a (Methods + 'a),
}
fn main() {
let methods: [&Methods; 2] = [&Methods_0, &Methods_1];
let mut obj = Object { methods: methods[0] };
obj.methods.func();
obj.methods = methods[1];
obj.methods.func();
}
Now, what if there are hundreds of such implementations? E.g. imagine implementations of cards for collectible card game where every card does something completely different and is hard to generalize; or imagine implementations for opcodes for a huge state machine. Sure you can argue that a different design pattern can be used -- but that's not the point of this question...
Wonder if there is any way for these Impl structs to somehow "register" themselves so they can be looked up later by a factory method? I would be happy to end up with a magical macro or even a plugin to accomplish that.
Say, in D you can use templates to register the implementations -- and if you can't for some reason, you can always inspect modules at compile-time and generate new code via mixins; there are also user-defined attributes that can help in this. In Python, you would normally use a metaclass so that every time a new child class is created, a ref to it is stored in the metaclass's registry which allows you to look up implementations by name or parameter; this can also be done via decorators if implementations are simple functions.
Ideally, in the example above you would be able to create Object as
Object::new(0)
where the value 0 is only known at runtime and it would magically return you an Object { methods: &Methods_0 }, and the body of new() would not have the implementations hard-coded like so "methods: [&Methods; 2] = [&Methods_0, &Methods_1]", instead it should be somehow inferred automatically.
So, this is probably extremely buggy, but it works as a proof of concept.
It is possible to use Cargo's code generation support to make the introspection at compile-time, by parsing (not exactly parsing in this case, but you get the idea) the present implementations, and generating the boilerplate necessary to make Object::new() work.
The code is pretty convoluted and has no error handling whatsoever, but works.
Tested on rustc 1.0.0-dev (2c0535421 2015-02-05 15:22:48 +0000)
(See on github)
src/main.rs:
pub mod implementations;
mod generated_glue {
include!(concat!(env!("OUT_DIR"), "/generated_glue.rs"));
}
use generated_glue::Object;
pub trait Methods {
fn func(&self);
}
pub struct Methods_2;
impl Methods for Methods_2 {
fn func(&self) {
println!("baz");
}
}
fn main() {
Object::new(2).func();
}
src/implementations.rs:
use super::Methods;
pub struct Methods_0;
impl Methods for Methods_0 {
fn func(&self) {
println!("foo");
}
}
pub struct Methods_1;
impl Methods for Methods_1 {
fn func(&self) {
println!("bar");
}
}
build.rs:
#![feature(core, unicode, path, io, env)]
use std::env;
use std::old_io::{fs, File, BufferedReader};
use std::collections::HashMap;
fn main() {
let target_dir = Path::new(env::var_string("OUT_DIR").unwrap());
let mut target_file = File::create(&target_dir.join("generated_glue.rs")).unwrap();
let source_code_path = Path::new(file!()).join_many(&["..", "src/"]);
let source_files = fs::readdir(&source_code_path).unwrap().into_iter()
.filter(|path| {
match path.str_components().last() {
Some(Some(filename)) => filename.split('.').last() == Some("rs"),
_ => false
}
});
let mut implementations = HashMap::new();
for source_file_path in source_files {
let relative_path = source_file_path.path_relative_from(&source_code_path).unwrap();
let source_file_name = relative_path.as_str().unwrap();
implementations.insert(source_file_name.to_string(), vec![]);
let mut file_implementations = &mut implementations[*source_file_name];
let mut source_file = BufferedReader::new(File::open(&source_file_path).unwrap());
for line in source_file.lines() {
let line_str = match line {
Ok(line_str) => line_str,
Err(_) => break,
};
if line_str.starts_with("impl Methods for Methods_") {
const PREFIX_LEN: usize = 25;
let number_len = line_str[PREFIX_LEN..].chars().take_while(|chr| {
chr.is_digit(10)
}).count();
let number: i32 = line_str[PREFIX_LEN..(PREFIX_LEN + number_len)].parse().unwrap();
file_implementations.push(number);
}
}
}
writeln!(&mut target_file, "use super::Methods;").unwrap();
for (source_file_name, impls) in &implementations {
let module_name = match source_file_name.split('.').next() {
Some("main") => "super",
Some(name) => name,
None => panic!(),
};
for impl_number in impls {
writeln!(&mut target_file, "use {}::Methods_{};", module_name, impl_number).unwrap();
}
}
let all_impls = implementations.values().flat_map(|impls| impls.iter());
writeln!(&mut target_file, "
pub struct Object;
impl Object {{
pub fn new(impl_number: i32) -> Box<Methods + 'static> {{
match impl_number {{
").unwrap();
for impl_number in all_impls {
writeln!(&mut target_file,
" {} => Box::new(Methods_{}),", impl_number, impl_number).unwrap();
}
writeln!(&mut target_file, "
_ => panic!(\"Unknown impl number: {{}}\", impl_number),
}}
}}
}}").unwrap();
}
The generated code:
use super::Methods;
use super::Methods_2;
use implementations::Methods_0;
use implementations::Methods_1;
pub struct Object;
impl Object {
pub fn new(impl_number: i32) -> Box<Methods + 'static> {
match impl_number {
2 => Box::new(Methods_2),
0 => Box::new(Methods_0),
1 => Box::new(Methods_1),
_ => panic!("Unknown impl number: {}", impl_number),
}
}
}