Box and array

README.md

@@ -1,28 +1,3 @@
-Intermediate problem:
-
-```rust
-pub struct Equals<'a> {
-  field: &'a str,
-  value: Value
-}
-
-impl Equals<'_> {
-  pub fn from_args(mut args: ModuleArgs) -> Equals {
-    Equals {
-      field: match args.remove("field") {
-        Some(Value::Str(s)) => s,
-        _ => panic!("The Equals filter needs a field to filter in “field”")
-      },
-      value: args.remove("value").expect("The Equals filter needs a reference value in “value”")
-    }
-  }
-}
-```
-
-Error on `Some(Value::Str(s)) => s` even though `args` is mutable and trashed at the end of the function.
-
-<hr>
-
 ## setup
 
 In module `modules`, I have:
@@ -36,15 +11,15 @@ pub trait Module {
 In module `filters`, I have:
 
 ```rust
-pub struct Equals<'a> { … }
+pub struct Equals { … }
 
-impl Equals<'_> {
+impl Equals {
   pub fn from_args(mut args: ModuleArgs) -> Equals {
     Equals { … }
   }
 }
 
-impl Module for Equals<'_> {
+impl Module for Equals {
   fn run(&self, record: &mut Record) -> Result<bool, ()> { … }
 }
 ```
@@ -55,37 +30,39 @@ What I really want (for a start) is that, in module `modules`:
 
 ```rust
 struct Available {
-  name: &'static str,
+  name: String,
-  cons: fn(ModuleArgs) -> dyn Module
+  cons: Box<fn(ModuleArgs) -> dyn Module>
 }
 
-const available: (Available) = (
+const available: [Available] = [
-  Available{ name: "equals", cons: move |a| filters::Equals::from_args(a) }
+  Available { name: "equals", cons: Box.new(filters::Equals::from_args) }
-);
+];
 ```
 
-with `available` being a tuple of available modules, each having a name and a constructor.
+with `available` being an array of available modules, each having a name and a constructor.
 
 ## problem
 
-The above code gives me two errors:
+The above code gives me these errors (which I suspect are hiding the next error about `"equals"` probably being `&str` instead of `String`…):
 
-1. one I somewhat understand:
+* first:
 
-   ```
+  ```
-   error[E0277]: the size for values of type `(dyn modules::Module + 'static)` cannot be known at compilation time
+  error[E0423]: expected value, found struct `Box`
-     --> src/modules.rs:10:45
+    --> src/modules.rs:10:37
-      |
+     |
-   10 |   Available{ name: "equals", cons: move |a| filters::Equals::from_args(a) }
+  10 |   Available { name: "equals", cons: Box.new(filters::Equals::from_args) }
-      |                                             ^ doesn't have a size known at compile-time
+     |                                     ^^^ constructor is not visible here due to private fields
-   ```
+  ```
 
-2. and one I don’t understand:
+* second:
 
-   ```
+  ```
-   error[E0308]: mismatched types
+  error[E0277]: the size for values of type `[modules::Available]` cannot be known at compilation time
-     --> src/modules.rs:10:45
+   --> src/modules.rs:9:18
-      |
+    |
-   10 |   Available{ name: "equals", cons: move |a| filters::Equals::from_args(a) }
+  9 | const available: [Available] = [
-      |                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected trait modules::Module, found struct `filters::Equals`
+    |                  ^^^^^^^^^^^ doesn't have a size known at compile-time
-   ```
+    |
+    = help: the trait `std::marker::Sized` is not implemented for `[modules::Available]`
+  ```