Enum MessageCategory 

#[non_exhaustive]
pub enum MessageCategory {
    SystemInstruction,
    ToolDefinition,
    Context,
    History,
    Current,
    ToolResult,
}

Semantic category of a message for provider-specific handling.

Categories help providers optimize message processing, especially for caching. Messages with different categories may be grouped, cached, or prioritized differently.

Priority Defaults

When using semantic constructors like UnifiedMessage::system_instruction(), categories automatically set appropriate priority values:

Category	Default Priority	Cacheable
SystemInstruction	0 (highest)	Yes
ToolDefinition	1	Yes
Context	5	Yes
History	20	Yes
ToolResult	26	No
Current	30 (lowest)	No

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

SystemInstruction

Core system prompts and instructions.

These are the foundational instructions that define the model’s behavior. They’re almost always cached since they rarely change within a session.

ToolDefinition

Tool/function definitions.

Contains the schema definitions for available tools. Typically cached since tool definitions are static for a given application.

Context

Contextual information (user preferences, session state, etc.).

Background context that informs responses but isn’t part of the direct conversation. Often cached for the session duration.

History

Conversation history (previous turns).

Past messages in the conversation. May be partially cached for long conversations to save on repeated processing.

Current

Current user input (the active turn).

The message being responded to right now. Never cached since it changes with each request.

ToolResult

Results from tool executions.

Output from function calls. Not cached since tool results are dynamic and request-specific.

Trait Implementations

impl Clone for MessageCategory

fn clone(&self) -> MessageCategory

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for MessageCategory

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for MessageCategory

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Hash for MessageCategory

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for MessageCategory

fn eq(&self, other: &MessageCategory) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for MessageCategory

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl Eq for MessageCategory

impl StructuralPartialEq for MessageCategory