MessagePlaceholder constructor

const MessagePlaceholder({
  1. required String variableName,
})

Prompt template that accepts one ChatMessage or an ordered message list (ChatMessageType.messagePlaceholder).

This is useful when the value can be either a single runtime-selected message or a group of messages that must stay at the same prompt position.

Example:

ChatPromptTemplate.fromPromptMessages([
  ChatMessagePromptTemplate.system('You are a helpful AI assistant'),
  ChatMessagePromptTemplate.messagesPlaceholder('history'),
  ChatMessagePromptTemplate.messagePlaceholder('input'),
]);

Alternatively, you can use ChatPromptTemplate.fromTemplates to achieve the same result.

final promptTemplate = ChatPromptTemplate.fromTemplates([
  (ChatMessageType.system, 'You are a helpful AI assistant'),
  (ChatMessageType.messagesPlaceholder, 'history'),
  (ChatMessageType.messagePlaceholder, 'input'),
]);

Implementation

const MessagePlaceholder({required this.variableName})
  : super(
      prompt: const PromptTemplate(inputVariables: {}, template: ''),
    );