Kotlin 将带大括号和不带大括号的Lambda值赋给@Composable函数

我正在关注一个Android开发者Codelab.我将此代码片段转换为可组合的:

            OutlinedTextField(
                value = userGuess,
                singleLine = true,
                shape = shapes.large,
                modifier = Modifier.fillMaxWidth(),
                colors = TextFieldDefaults.colors(
                    focusedContainerColor = colorScheme.surface,
                    unfocusedContainerColor = colorScheme.surface,
                    disabledContainerColor = colorScheme.surface,
                ),
                onValueChange =  onUserGuessChanged ,
                label = { Text(stringResource(R.string.enter_your_word)) },
                isError = false,
                keyboardOptions = KeyboardOptions.Default.copy(
                    imeAction = ImeAction.Done
                ),
                keyboardActions = KeyboardActions(
                    onDone = { onKeyboardDone() }
                )
            )

OnUserGuessChanged和onKeyBoardDone都是lambdas.这是Composable函数的头

@Composable
fun myComposableFunction(
    onUserGuessChanged: (String) -> Unit,
    onKeyboardDone: () -> Unit,
    modifier: Modifier = Modifier
) { 
[...]

为什么onValueChanged必须不带大括号和函数括号赋值，而onDone必须同时赋值？？它们之间有什么特点或区别？