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: _tiering.rs
    path of file: ./repos/aws-sdk-rust/sdk/s3/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>The S3 Intelligent-Tiering storage class is designed to optimize storage costs by automatica
    
    pub fn build(self) -> ::std::result::Result<crate::types::Tiering, ::aws_smithy_types::error::operation::BuildError> {
        ::std::result::Result::Ok(crate::types::Tiering {
            days: self.days.ok_or_else(|| {
                ::aws_smithy_types::error::operation::BuildError::missing_field(
                    "days",
                    "days was not specified but it is required when building Tiering",
                )
            })?,
            access_tier: self.access_tier.ok_or_else(|| {
                ::aws_smithy_types::error::operation::BuildError::missing_field(
                    "access_tier",
                    "access_tier was not specified but it is required when building Tiering",
                )
            })?,
        })
    }