1. The usual --example#

When you run:

cargo run --example hello

Cargo assumes:

• You are in the root of a Cargo package (or workspace).
• The example is located in

my_project/
├── Cargo.toml
└── examples/
    └── hello.rs

or

examples/
    hello/
        main.rs

Cargo automatically looks inside the current package’s examples/ directory.

For example,

my_project/
├── Cargo.toml
├── src/
│   └── lib.rs
└── examples/
    ├── hello.rs
    └── world.rs

Then

cargo run --example hello

runs

examples/hello.rs

2. What --manifest-path does#

Your command is

cargo run --manifest-path examples/toasty-todo/Cargo.toml

Here, examples/toasty-todo is not an example target.

Instead, it is an entirely separate Cargo package.

Imagine a repository like

repository/
├── Cargo.toml
├── src/
│   └── ...
└── examples/
    ├── toasty-todo/
    │   ├── Cargo.toml
    │   └── src/
    │       └── main.rs
    └── calculator/
        ├── Cargo.toml
        └── src/

Notice that

examples/toasty-todo/

contains its own Cargo.toml.

That means it is an independent crate.

Cargo has no idea you want that crate unless you tell it which manifest to use.

So

cargo run --manifest-path examples/toasty-todo/Cargo.toml

means

“Use this Cargo.toml as the root package and run its binary.”

3. Why not --example toasty-todo?#

Because there is no example target named toasty-todo.

--example only works for examples declared by the current package, such as

examples/foo.rs

or

examples/foo/main.rs

It does not look for another Cargo package.

4. Why projects organize examples this way#

Some example applications are much larger than a simple examples/foo.rs.

For example, they may have

toasty-todo/
├── Cargo.toml
├── src/
├── assets/
├── migrations/
├── tests/
└── README.md

Using a full Cargo package allows them to have:

• their own dependencies
• their own features
• separate Cargo.toml
• build scripts
• tests
• assets
• multiple source files

This would be awkward or impossible with a single examples/foo.rs.

Summary#

So, in your case, examples/toasty-todo is a standalone Cargo package with its own manifest, not an example target. That’s why --manifest-path is used instead of --example.