You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: _workflow_execution.rs
    path of file: ./repos/aws-sdk-rust/sdk/swf/src/types
    
    the code of the file until where you have to start completion: // Code generated by software.amazon.smithy.rust.codegen.smithy-rs. DO NOT EDIT.

/// <p>Represents a workflow execution.</p>
#[non_exhaustive]
#[derive(::std::clone::Clone, ::std::cmp::PartialEq, ::std::fmt::Debug)]
pub struct WorkflowExecution {
    /// <p>The user defined identifier associated with the workflow execution.</p>
    pub workflow_id: ::std::string::String,
    /// <p>A system-generated unique identifier for the workflow execution.</p>
    pub run_id: ::std::string::String,
}
impl WorkflowExecu
    
    pub fn build(self) -> ::std::result::Result<crate::types::WorkflowExecution, ::aws_smithy_types::error::operation::BuildError> {
        ::std::result::Result::Ok(crate::types::WorkflowExecution {
            workflow_id: self.workflow_id.ok_or_else(|| {
                ::aws_smithy_types::error::operation::BuildError::missing_field(
                    "workflow_id",
                    "workflow_id was not specified but it is required when building WorkflowExecution",
                )
            })?,
            run_id: self.run_id.ok_or_else(|| {
                ::aws_smithy_types::error::operation::BuildError::missing_field(
                    "run_id",
                    "run_id was not specified but it is required when building WorkflowExecution",
                )
            })?,
        })
    }