# deviceFallbackRule

A device fallback rule record carrying requestedBackend, fallbackBackend, reason, notes.

Last updated: 2026-09-09

Package: compute.device | Status: source-declared

Tags: compute, compute.device, cpu, device, method, source-example, thing, yeho

Inspect device capability catalogs and model resource lifetimes and placement decisions.

```yh
external thing deviceFallbackRule
```

- text requestedBackend: Stores requested backend as text.
- text fallbackBackend: Stores fallback backend as text.
- text reason: Stores reason as text.
- text notes: Stores notes as text.
- deviceFallbackRule(text requestedBackend, text fallbackBackend, text reason, text notes): Device fallback rule.
- HasFallback() returns bool: Has fallback.
- Describe() returns text: Describe.

## Use deviceFallbackRule

A complete small caller. Values are illustrative; check the returned result and package requirements before connecting live resources.

Verification: type checked

```yh
using compute.device

// Inspect device capability catalogs and model resource lifetimes and placement decisions.
deviceFallbackRule sample = deviceFallbackRule("requested Backend", "fallback Backend", "reason", "notes")
Console.Log(Text.From(sample.requestedBackend))

```

Save this beside start.yh as project.mech:

```toml
manifestVersion = "2"
package = "api.example.compute_device__devicefallbackrule"
version = "0.1.0"
languageEdition = "yeho-core-2026.1"

[app]
kind = "headless"

[[dependencies]]
package = "compute.buffer"
version = "0.1.0"
path = "../../../yeho/packages/compute/buffer"

[[dependencies]]
package = "compute.device"
version = "0.1.0"
path = "../../../yeho/packages/compute/device"

[[dependencies]]
package = "compute.tensor"
version = "0.1.0"
path = "../../../yeho/packages/compute/tensor"

[[dependencies]]
package = "console"
version = "0.1.0"
path = "../../../yeho/packages/console"

[[dependencies]]
package = "diagnostics"
version = "0.1.0"
path = "../../../yeho/packages/diagnostics"

```

Extract the example archive beside the yeho and dolphin checkouts. This example requires those source dependencies and a current developer compiler.

```sh
./yeho/build/dolphin-metal/yehoc ./api-examples/compute.device--deviceFallbackRule/usage --backend cpu-oracle -o /tmp/yeho-example
/tmp/yeho-example
```


## deviceFallbackRule.HasFallback

A complete caller for this public method. Sample inputs are illustrative; native resources require their owning lifecycle.

Verification: type checked

```yh
using compute.device

// Has fallback.
deviceFallbackRule instance = deviceFallbackRule("requested Backend", "fallback Backend", "reason", "notes")
bool result = instance.HasFallback()
Console.Log(Text.From(result))

```

Save this beside start.yh as project.mech:

```toml
manifestVersion = "2"
package = "api.example.compute_device__devicefallbackrule"
version = "0.1.0"
languageEdition = "yeho-core-2026.1"

[app]
kind = "headless"

[[dependencies]]
package = "compute.buffer"
version = "0.1.0"
path = "../../../yeho/packages/compute/buffer"

[[dependencies]]
package = "compute.device"
version = "0.1.0"
path = "../../../yeho/packages/compute/device"

[[dependencies]]
package = "compute.tensor"
version = "0.1.0"
path = "../../../yeho/packages/compute/tensor"

[[dependencies]]
package = "console"
version = "0.1.0"
path = "../../../yeho/packages/console"

[[dependencies]]
package = "diagnostics"
version = "0.1.0"
path = "../../../yeho/packages/diagnostics"

```

Extract the example archive beside the yeho and dolphin checkouts. This example requires those source dependencies and a current developer compiler.

```sh
./yeho/build/dolphin-metal/yehoc ./api-examples/compute.device--deviceFallbackRule/method-HasFallback-5 --backend cpu-oracle -o /tmp/yeho-example
/tmp/yeho-example
```


## deviceFallbackRule.Describe

A complete caller for this public method. Sample inputs are illustrative; native resources require their owning lifecycle.

Verification: type checked

```yh
using compute.device

// Describe.
deviceFallbackRule instance = deviceFallbackRule("requested Backend", "fallback Backend", "reason", "notes")
text result = instance.Describe()
Console.Log(Text.From(result))

```

Save this beside start.yh as project.mech:

```toml
manifestVersion = "2"
package = "api.example.compute_device__devicefallbackrule"
version = "0.1.0"
languageEdition = "yeho-core-2026.1"

[app]
kind = "headless"

[[dependencies]]
package = "compute.buffer"
version = "0.1.0"
path = "../../../yeho/packages/compute/buffer"

[[dependencies]]
package = "compute.device"
version = "0.1.0"
path = "../../../yeho/packages/compute/device"

[[dependencies]]
package = "compute.tensor"
version = "0.1.0"
path = "../../../yeho/packages/compute/tensor"

[[dependencies]]
package = "console"
version = "0.1.0"
path = "../../../yeho/packages/console"

[[dependencies]]
package = "diagnostics"
version = "0.1.0"
path = "../../../yeho/packages/diagnostics"

```

Extract the example archive beside the yeho and dolphin checkouts. This example requires those source dependencies and a current developer compiler.

```sh
./yeho/build/dolphin-metal/yehoc ./api-examples/compute.device--deviceFallbackRule/method-Describe-6 --backend cpu-oracle -o /tmp/yeho-example
/tmp/yeho-example
```


Package presence and a declaration do not establish support on every host. Host services need their platform and lifecycle setup.

Source: yeho/packages/compute/device/device.yh

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