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: _math_activity.rs
    path of file: ./repos/aws-sdk-rust/sdk/iotanalytics/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>An activity that computes an arithmetic expression using the message's attributes.</p>
#[non_exhaustive]
#[derive(::std::clone::Clone, ::std::cmp::PartialEq, ::std::fmt::Debug)]
pub struct MathActivity {
    /// <p>The name of the math activity.</p>
    pub name: ::std::string::String,
    /// <p>The name of the attribute that contains the result of the math operation.</p>
    pub attribute: ::std::string::String,
    /// <p>An expr
    
    pub fn build(self) -> ::std::result::Result<crate::types::MathActivity, ::aws_smithy_types::error::operation::BuildError> {
        ::std::result::Result::Ok(crate::types::MathActivity {
            name: self.name.ok_or_else(|| {
                ::aws_smithy_types::error::operation::BuildError::missing_field(
                    "name",
                    "name was not specified but it is required when building MathActivity",
                )
            })?,
            attribute: self.attribute.ok_or_else(|| {
                ::aws_smithy_types::error::operation::BuildError::missing_field(
                    "attribute",
                    "attribute was not specified but it is required when building MathActivity",
                )
            })?,
            math: self.math.ok_or_else(|| {
                ::aws_smithy_types::error::operation::BuildError::missing_field(
                    "math",
                    "math was not specified but it is required when building MathActivity",
                )
            })?,
            next: self.next,
        })
    }