Is there an ergonomic way of initializing a struct in this situation?

[rustedrobot]

I have a couple structs in my code that look like this:

struct MyStruct {
    // This type doesn't have a default value
    non_default_value: NonDefaultValue,
    // around 10 fields that do have a default value
    f1: f32,
    f2: f32,
    ...
}

It isn't possible to create an instance of this struct like this because ..Default::default() syntax only works inside structs which implement Default which this struct cannot do since it has a field with non default value:

// Doesn't work
MyStruct {
    non_default_value,
    ..Default::default()
}

Is there a concise way of telling the compiler that I want the rest of the fields to have their default values. In C/C++ I can just leave the fields uninitialized. I have encountered this issue one too many times recently and the boilerplate has become frustrating.

[hax10]

There is an RFC for this feature, but I don't believe it's been implemented yet. For details, see:

Implementing partial default trait on structs

Hi everyone, Stuck with another one, if someone can share a better way please. struct SomeHolder { len: u32, type: String, common_holder: Box<CommonHolder> } impl Default for SomeHolder { fn default() -> Self { SomeHolder{type: "UNKNOWN".to_string(), ..Default::default()} } } warning: function cannot return without recursing --> src/main.rs:34:5 | 34 | fn default() -> Self { | ^^^^^^^^^^^^^^^^^^^^ cannot return without recur…

Also, I don't know if the partial_default crate is useful, but it may be worth a look.

[paramagnetic]

If you don't want the literal FRU syntax, you can just write a constructor method and use it instead of literals.

Or, you can pull out the fields with a default value into another struct.